std 160 ppr2 draft (chair approved rev1)
TRANSCRIPT
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BSRASHRAE Standard 160P
Public ReviewDraft
_____________________________________
ASHRAE Standard
Proposed New Standard160 Design Cri teria for Moistu re-Contro l Design
Analysis in Bui ld ings
Second Public Review (September 2008)(Draft Shows Independent Substantive
Changes To First Public Review Draft)
This draft has been recommended for public review bythe responsible project committee To submit acomment on this proposed standard go to the ASHRAEwebsite at httpwwwashraeorgtechnologypage331 and access the online comment database The draft issubject to modification until it is approved for publication by the ASHRAE Board of Directors andANSI The current edition of any standard may bepurchased from the ASHRAE Bookstore httpwwwashraeorg or by calling 404-636-8400 or 1-800-527-4723 (for orders in the US or Canada)
The appearance of any technical data or editorialmaterial in this public review document does not
constitute endorsement warranty or guaranty byASHRAE of any product service process procedure or design and ASHRAE expressly disclaims such
copy September 12 2008 This draft is covered under ASHRAE copyright Permission to reproduce or redistribute all or any part of this document must beobtained from the ASHRAE Manager of Standards 1791Tullie Circle NE Atlanta GA 30329 Phone 404-636-8400 Ext 1125 Fax 404-321-5478 E-mailstandardssectionashraeorg
AMERICAN SOCIETY OF HEATING REFRIGERATINGAND AIR-CONDITIONING ENGINEERS INC1791 Tullie Circle NE Atlanta GA 30329-2305
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 2 of 24
CONTENTS
BSRASHRAE Standard 160P
Criteria for Moisture-Control Design Analysis in Buildings
(Second Public Review Draft)
Section
Foreword
1 Purpose
2 Scope
3 Definitions Abbreviations and Symbols
4 Criteria for Design Parameters
5 Criteria for Selecting Analytical Procedures
6 Moisture Performance Evaluation Criteria7 Reporting
8 References
Informative Annex A Flow ChartsInformative Annex B Commentary on Standard 160
Informative Annex C Bibliography
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
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(This foreword is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
FOREWORD Although the majority of new buildings are safe comfortable and designed to provide effective protection
against moisture-related problems there are a certain number of buildings built each year that do experiencemoisture or mold problems Whether this number is now increasing and whether the increase is due to the greater emphasis on energy-efficiency measures today is a widely debated topic This standard is not concerned to answer
either of these questions but to provide guidance on how to best design buildings with adequate moisture control
features Given its position as a leader in the proper design of heating ventilating and air conditioning
equipment ASHRAE is uniquely qualified to provide such guidance
During the last two decades a number of computer simulation tools were developed to predict thermal
and moisture conditions in buildings and the building envelope In addition to their use as forensic tools in the
investigation of building failures these computer models are increasingly used to make recommendations for
building design in various climates However results obtained with these models are extremely sensitive to the
assumed moisture boundary conditions For instance during winter in cold climates the moisture conditions in
walls depend greatly on the indoor humidity conditions Thus a consistent approach to moisture design demands a
consistent framework for design assumptions or assumed ldquoloadsrdquo The question whether or not design features such as vapor retarders or ventilation systems are necessary cannot be answered objectively unless there is a
consensus definition of the interior and exterior moisture boundary conditions that the building is expected to be
able to sustain without negative consequences to itself or its inhabitants This standard formulates design
assumptions for moisture design analysis and criteria for acceptable performance
Ideally a design analysis involves the determination of the probability of failure treating all design
parameters and loads as stochastic variables However sufficient data are often not available to make a full
statistical treatment practical Instead a moisture design protocol will have to be based on a combination of
statistical data and professional judgment where only limited data exist Another judgment involves the choice of
an acceptable probability of the occurrence of damage Although it is common to impose very stringent criteria for
structural design because of safety concerns moisture damage usually occurs over a long period of time and
usually has less catastrophic although sometimes costly consequences An international consensus has emerged
that the analysis should be predicated on loads that will not be exceeded 90 of the time This standard hasadopted this approach
In a moisture analysis for building envelope design the choice of indoor environmental conditions is
extremely important especially for buildings in cold climates This standard opts for a design indoor climate
definition that is based on engineering principles is independent of construction and reflects the influence of
ventilation and air-conditioning equipment and controls that may or may not be part of the building design In
buildings where indoor humidity and temperature are explicitly controlled the building envelope performance
should be evaluated with the intended indoor design conditions In residential buildings indoor humidity is rarely
explicitly controlled and default design assumptions are needed for these buildings In general the standard
encourages designers to use their own design parameter values if they are known and part of the design If they
are unknown or not included in the design the standard provides default values for those loads and parameters
The standard does not address design details that deal with rainwater intrusion plumbing leaks ground
water and water damage caused by natural disasters such as floods and hurricanes While proper design for suchevents is extremely important and damage from such events involves a large percentage of moisture damage in
buildings these issues can be more effectively addressed by codes training of the trades and specific design
guidelines (see Commentary) This standard assumes that appropriate measures have been taken to limit bulk
water entry into the building and building envelope The standard does not intend to replace the judgment of the
design professional Rather it provides a framework for the design professional to identify and consider factors
that are important to the durability and serviceability of the building In addition many items in this standard are
based on incomplete information and are therefore partially based on the best professional judgment of the
standard committee at the time of writing this standard The development of this standard has pointed to many
unanswered questions questions that will hopefully be addressed and answered by research in the near future
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 4 of 24
Note to Reviewers This second publ ic review draf t makes independent substant ive changes to the fi rst
publi c review draft These changes are indicated in the text by underl in ing (for additi ons) and
str ikethrough (for deletions) Only these changes to the previous draft are open for review and
comment at th is time Additional material i s provided for context only and is not open f or comment
except as it relates to the proposed substantive changes
1 PURPOSE
The purpose of this standard is to specify performance-based design criteria for predicting mitigating or
reducing moisture damage to the building envelope materials components systems and furnishings depending on
climate construction type and HVAC system operation These criteria include
(a) criteria for selecting analytic procedures
(b) criteria for inputs and
(c) criteria for evaluation and use of outputs
2 SCOPE
21 This standard applies to the design of new buildings and to the retrofit and renovation of existing
buildings
22 This standard applies to all types of buildings building components and materials
23 This standard applies to all interior and exterior zones and building envelope cavities B-1
24 This standard does not directly apply to thermal comfort or acceptable indoor air quality B-1
25 This standard does not address the design of building components or envelopes to resist liquid water
leakage from sources such as rainwater ground water flooding or ice damsB-1
Note All superscript notes such as B-1 B-2 and so forth refer to commentary on the standard that is
contained in Informative Annex B
3 DEFINITIONS ABBREVIATIONS AND SYMBOLS
31 Definitions
24-hour r unn ing average a continuously updated average of values over the most recent 24 hours
7-day runn ing average a continuously updated average of values over the most recent 7 days
30-day running average a continuously updated average of values over the most recent 30 days
air tight construction construction in which the building envelope is designed with a continuous air barrier flow
retarder systemB-2
as-built the condition of a building assembly in a completed structure that accounts for an expected level of
deviation from the ideal construction of that assembly to address construction tolerances discontinuities and
minor defects
continuous air barr ier the combination of interconnected materials assemblies and flexible sealed joints and
components of the building envelope that provide air-tightness
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
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EMC80 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 80 RH at 20C (68F)
EMC90 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 90 RH at 20C (68F)
fi ber saturation the stage in wetting and drying of wood at which the cell walls are saturated and the cell cavities
are free from water
Low-slope roof roof with a slope of less than 1 in 6 or 12deg
Moisture Design Reference Years the 10th-percentile warmest and 10th-percentile coldest years from a 30-year
weather analysisB-3
residential pertaining to single-family or multi-family dwellings including high-rise residential buildings and
manufactured homes
rain runoff the rainwater contribution that is drained from building elements above the element under consideration
Steep-slope roof roof with a slope equal to or greater than 1 in 6 or 12deg
sur face relati ve humidi ty the equilibrium relative humidity of air in contact with a surface of a given moisture
content
water-resistive barr ier a continuous material layer other than the exterior surface within a wall assembly the
purpose of which is to resist the inward migration of liquid water
32 Abbreviations and Symbols
c = 136 times 105 m2s2 (107 inHgft3lb)
F D = rain deposition factor
F E = rain exposure factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
g = gravitational acceleration constant 981 ms2 (322 fts2) H = height of the building m (ft)
m = design moisture generation rate kgs (lbh)
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (inHg)
Δ P s
= design stack pressure Pa (in of water)
Q = ventilation rate m3s (cfm)
r h = rainfall intensity on a horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) [lb(ft2h)]
T i = indoor temperature ordmC or K (ordmF or ordmR)
T o = outdoor temperature ordmC or K (ordmF or ordmR)
T o24h = 24-hour running average outdoor temperature ordmC (ordmF)
T odaily = daily average outdoor temperature ordmC (ordmF)
U = hourly average wind speed at 10 m above ground level ms (mph)
V = building volume m3 (ft3)
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Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
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wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis kgkg (lblb)
= density of outdoor air kgm3 (lbft3)
= angle between wind direction and normal to the wall (see Figure 461)
4 CRITERIA FOR DESIGN PARAMETERS
This section provides criteria for selecting design values for initial moisture conditions indoor
temperatures indoor humidity air pressure air flows weather data and rain loads
41 Design Initial Moisture ConditionsContent of Building Materials
The initial moisture content of construction materials in new construction to be used in calculations for this
standard shall be two times EMC90 for concrete and two times EMC80 for all other materials unless procedures to
dry construction materials andor procedures to protect construction materials and assemblies from wetting during
construction are specified in which case EMC90 for concrete and EMC80 for all other materials shall be used In
retrofit applications EMC90 for concrete and EMC80 for all other materials shall be used unless measured
moisture content values are availableB-4
42 Indoor Design TemperatureIf the design or operating specifications for the building specify indoor operating temperatures or the
indoor design temperatures are specified by applicable code regulation or law these temperatures shall be used
Otherwise the indoor temperatures specified in Table 42 shall be used B-5
TABLE 42 Indoor Design Temperature24-hour running average of
outdoor temperature
Indoor Design Temperature degC (degF)
Heating only Heating and air-conditioning
To 24h le 183degC
(To 24h le 65degF)
211degC
(70degF)
211 degC
(70degF)
183degC lt To 24h le 211degC
(65degF lt To 24h le 70degF)
To 24h + 28degC
(To 24h+5degF)
To 24h + 28degC
(To 24h+5degF)
To 24hgt211degC (70degF)
(To 24hgt70degF)
To 24h + 28degC
(To 24h+5degF)
239degC
(75degF)
Note To 24h = 24-hour average outdoor temperature
43 Indoor Design Humidity
If the HVAC equipment and controls are included in the design the intended design indoor humidity shall
be used If no such provisions are made then indoor design humidity shall be determined by one of three methods(a) Simplified Method (in accordance with Section 431)
(b) Intermediate Method (in accordance with Section 432) or
(c) Full Parameter Calculation (in accordance with Section 433)
The indoor design humidity shall be checked for compliance with applicable standards such asANSIASHRAE Standard 551 If calculated design humidity is outside the ranges specified measures shall be
taken to bring the humidity within the specified range
431 Indoor Design Humidity Simplified Method
Design indoor humidity according to the simplified method is a function of average daily outdoor
temperature and is given in Table 431 (Figure 431) B-6
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
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Table 431 Design indoor RH Simplified Method
Note To daily = Daily average outdoor temperature
- 20 - 10 0 10 20 30 20
30
40
50
60
70
80
I n d o o r D e s i g n R H [ ]
Daily Average Outdoor Temperature [degC]
68
Daily Average Outdoor Temperature [degF]
14
Figure 431 Design indoor relative humidity Simplified Method
432 Indoor Design Humidity Intermediate Method In this method indoor design humidity is determined
from hourly weather and depends on the season (Section 42) and the type of HVAC equipment
4321 Indoor Design Humidity without Dehumidification or Air-conditioning This section applies during
heating and temperature ldquofloatrdquo conditions as determined in Section 42 when cooling and dehumidification
equipment is not present or not operating Indoor vapor pressure for moisture design purposes shall be determined
using the following mass balance equation B-7
Q
mc p p h oi
24
(4-1)
where
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (in Hg)
c = 136 times 105 Pamiddotm3kg (107 inHgmiddotft3lb)
m = design moisture generation rate kgs (lbh) (in accordance with Sections 43211 and 2)
Q = design ventilation rate m3s (cfm) (in accordance with Sections 43213 and 4)
Daily Average
Outdoor Temperature
degC
Design RH
(Based on degC)
Daily Average
Outdoor Temperature
degF
Design RH
(Based on degF)
Below -10degC 40 Below 14degF 40
-10degCle To dailyle 20degC 40 + (To daily+10) 14degFle To dailyle 68degF 40 + (To daily-14)18Above 20degC 70 Above 68degF 70
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
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43211 Residential Moisture Generation Design values for residential moisture generation
m are based
on the expected number of occupants For design purposes a minimum of two occupants is assumed with an
additional occupant for each bedroom in addition to the master bedroom Design moisture generation rates are
given in Table 432 B-8
Table 432 Residential design moisture generation rates Number of
Bedrooms Number of Occupants
Moisture generation rate
1 bedroom 2 8 Lday 09 x 10-4 kgs 07 lbh
2 bedrooms 3 12 Lday 14 x 10-4 kgs 11 lbh
3 bedrooms 4 14 Lday 16 x 10-4 kgs 13 lbh
4 bedrooms 5 15 Lday 17 x 10-4 kgs 14 lbh
Additional bedrooms +1 per bedroom +1 Lday +01 x 10-4 kgs +01 lbh
If the home contains a jetted tub installed in a room without an automatically controlled (eg humidistat) exhaust
fan add 13 Lday or 015 x 10-4 kgs (012 lbh)
43212 Moisture Generation for Other Occupancies For other occupancies moisture generationdesign values shall be appropriate for the intended use of the building If the appropriate moisture generation rates
are not available for the intended use the simplified method (Section 431) shall be used
43213 Designed Ventilation Design ventilation rates shall be used for the calculation of design indoor
vapor pressure (Equation 4-1) The design ventilation rate to be used is the expected continuous ventilation rate
For intermittent ventilation systems ventilation effectiveness shall be accounted for according to ANSIASHRAE
Standard 6222
43214 Non-Designed Ventilation In buildings without a designed ventilation system the following
default ventilation rates shall be used for purposes of calculating the design indoor vapor pressure (Equation 4-1)
B-9
New buildings standard construction air exchange rate of 02 ach
Q = 56 x 10-5 V m3 s (4-2a)
where V is the building volume (m3) or
Q = 00033V cfm (4-2b)
where V is the building volume (ft3)
New buildings airtight construction air exchange rate of 01 ach
Q = 28 x 10-5
V m3
s (4-3a)
where V is the building volume (m3) or
Q = 00017V cfm (4-3b)
where V is building volume (ft3)
4322 Indoor Design Humidity with Air-Conditioning If the air-conditioning equipment is running and is
controlled solely by thermostat the design indoor humidity shall be derived from the following equation
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 9 of 24
wi= 0004+04w0 (4-4)
where
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis
kgkg (lblb) B-10
If the building is air-conditioned with humidity-controlled equipment the indoor humidity design
conditions shall be the specified humidity control setting or the humidity calculated with Equation 4-4 whichever
is lower If no humidity control setting is specified the control setting shall be 50 RH
4323 Indoor Design Humidity with Dehumidification without Air-Conditioning If the building is designed
to be dehumidified with humidity-controlled dehumidification equipment and cooling equipment is not present or
not operating the indoor design humidity shall be the humidity control setting or the humidity calculated with
Equation 4-1 whichever is lower If no humidity control setting is specified the control setting shall be 50 RH
433 Indoor Design Humidity Full Parametric Calculation Full parametric evaluation of indoor humidity
requires comprehensive inputs to support the analysis of the hygrothermal response and dynamic hygrothermal
flux contribution of building elements finishes and furniture (hygric buffering) The analysis shall include thermaland mass balances and shall use simulation algorithms and time-step intervals that capture hygrothermal response
of sensitive materials and conditions
Required inputs include(a) hygrothermal properties of building materials finishes and furniture
(b) design initial moisture conditions (in accordance with Section 41)
(c) design indoor temperatures (in accordance with Section 42)
(d) design ventilation rates (in accordance with Section 43213 or 43214)
(e) design moisture generation rates (in accordance with Section 43211 or 43212)
(f) effect of active dehumidification systems
(g) design pressure data (in accordance with Section 441)
(h) design weather data (in accordance with Section 45)(i) design rain loads (in accordance with Section 46)
44 Design Air Pressure Differentials and Flows
Analysis of the effect of air pressure differentials and air flows is optional If the effect is not considered in
the design analysis this shall be expressly stated in the report If the effect is included Section 441 shall apply
441 Effect of Air Pressure Differentials Included in Design Analysis If the indoor air pressure differential
between indoors and outdoors is controlled that air pressure differential shall be used in the design analysis B-11
If the indoor air pressure differential is not managed one of two alternative procedures shall be followed
4411 Design Air Pressure Differential Alternative 1 The design air pressure differential shall be calculated
from design ventilation rates including the planned fresh air supply and exhaust rates the building air tightnesswind pressures using Moisture Design Weather Data (Section 45) and stack pressure (Section 4413)
4412 Design Air Pressure Differential Alternative 2 A design indoor air pressure differential of +5 Pa (002
in wc) above outdoor air pressure (air flow to the exterior) shall be assumed used when the 24-hour running
average outdoor temperature is below the indoor design temperatureduring the heating season and ndash 5 Pa (air flow
to the interior) when the 24-hour running average outdoor temperature is above the indoor design temperature
during the cooling season B-12
Stack pressure differential at the top of the wall of the top floor shall be calculated (Section 4413) for buildings
taller than three stories and used as the design indoor pressure differential if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
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4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
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5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 2 of 24
CONTENTS
BSRASHRAE Standard 160P
Criteria for Moisture-Control Design Analysis in Buildings
(Second Public Review Draft)
Section
Foreword
1 Purpose
2 Scope
3 Definitions Abbreviations and Symbols
4 Criteria for Design Parameters
5 Criteria for Selecting Analytical Procedures
6 Moisture Performance Evaluation Criteria7 Reporting
8 References
Informative Annex A Flow ChartsInformative Annex B Commentary on Standard 160
Informative Annex C Bibliography
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 3 of 24
(This foreword is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
FOREWORD Although the majority of new buildings are safe comfortable and designed to provide effective protection
against moisture-related problems there are a certain number of buildings built each year that do experiencemoisture or mold problems Whether this number is now increasing and whether the increase is due to the greater emphasis on energy-efficiency measures today is a widely debated topic This standard is not concerned to answer
either of these questions but to provide guidance on how to best design buildings with adequate moisture control
features Given its position as a leader in the proper design of heating ventilating and air conditioning
equipment ASHRAE is uniquely qualified to provide such guidance
During the last two decades a number of computer simulation tools were developed to predict thermal
and moisture conditions in buildings and the building envelope In addition to their use as forensic tools in the
investigation of building failures these computer models are increasingly used to make recommendations for
building design in various climates However results obtained with these models are extremely sensitive to the
assumed moisture boundary conditions For instance during winter in cold climates the moisture conditions in
walls depend greatly on the indoor humidity conditions Thus a consistent approach to moisture design demands a
consistent framework for design assumptions or assumed ldquoloadsrdquo The question whether or not design features such as vapor retarders or ventilation systems are necessary cannot be answered objectively unless there is a
consensus definition of the interior and exterior moisture boundary conditions that the building is expected to be
able to sustain without negative consequences to itself or its inhabitants This standard formulates design
assumptions for moisture design analysis and criteria for acceptable performance
Ideally a design analysis involves the determination of the probability of failure treating all design
parameters and loads as stochastic variables However sufficient data are often not available to make a full
statistical treatment practical Instead a moisture design protocol will have to be based on a combination of
statistical data and professional judgment where only limited data exist Another judgment involves the choice of
an acceptable probability of the occurrence of damage Although it is common to impose very stringent criteria for
structural design because of safety concerns moisture damage usually occurs over a long period of time and
usually has less catastrophic although sometimes costly consequences An international consensus has emerged
that the analysis should be predicated on loads that will not be exceeded 90 of the time This standard hasadopted this approach
In a moisture analysis for building envelope design the choice of indoor environmental conditions is
extremely important especially for buildings in cold climates This standard opts for a design indoor climate
definition that is based on engineering principles is independent of construction and reflects the influence of
ventilation and air-conditioning equipment and controls that may or may not be part of the building design In
buildings where indoor humidity and temperature are explicitly controlled the building envelope performance
should be evaluated with the intended indoor design conditions In residential buildings indoor humidity is rarely
explicitly controlled and default design assumptions are needed for these buildings In general the standard
encourages designers to use their own design parameter values if they are known and part of the design If they
are unknown or not included in the design the standard provides default values for those loads and parameters
The standard does not address design details that deal with rainwater intrusion plumbing leaks ground
water and water damage caused by natural disasters such as floods and hurricanes While proper design for suchevents is extremely important and damage from such events involves a large percentage of moisture damage in
buildings these issues can be more effectively addressed by codes training of the trades and specific design
guidelines (see Commentary) This standard assumes that appropriate measures have been taken to limit bulk
water entry into the building and building envelope The standard does not intend to replace the judgment of the
design professional Rather it provides a framework for the design professional to identify and consider factors
that are important to the durability and serviceability of the building In addition many items in this standard are
based on incomplete information and are therefore partially based on the best professional judgment of the
standard committee at the time of writing this standard The development of this standard has pointed to many
unanswered questions questions that will hopefully be addressed and answered by research in the near future
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Note to Reviewers This second publ ic review draf t makes independent substant ive changes to the fi rst
publi c review draft These changes are indicated in the text by underl in ing (for additi ons) and
str ikethrough (for deletions) Only these changes to the previous draft are open for review and
comment at th is time Additional material i s provided for context only and is not open f or comment
except as it relates to the proposed substantive changes
1 PURPOSE
The purpose of this standard is to specify performance-based design criteria for predicting mitigating or
reducing moisture damage to the building envelope materials components systems and furnishings depending on
climate construction type and HVAC system operation These criteria include
(a) criteria for selecting analytic procedures
(b) criteria for inputs and
(c) criteria for evaluation and use of outputs
2 SCOPE
21 This standard applies to the design of new buildings and to the retrofit and renovation of existing
buildings
22 This standard applies to all types of buildings building components and materials
23 This standard applies to all interior and exterior zones and building envelope cavities B-1
24 This standard does not directly apply to thermal comfort or acceptable indoor air quality B-1
25 This standard does not address the design of building components or envelopes to resist liquid water
leakage from sources such as rainwater ground water flooding or ice damsB-1
Note All superscript notes such as B-1 B-2 and so forth refer to commentary on the standard that is
contained in Informative Annex B
3 DEFINITIONS ABBREVIATIONS AND SYMBOLS
31 Definitions
24-hour r unn ing average a continuously updated average of values over the most recent 24 hours
7-day runn ing average a continuously updated average of values over the most recent 7 days
30-day running average a continuously updated average of values over the most recent 30 days
air tight construction construction in which the building envelope is designed with a continuous air barrier flow
retarder systemB-2
as-built the condition of a building assembly in a completed structure that accounts for an expected level of
deviation from the ideal construction of that assembly to address construction tolerances discontinuities and
minor defects
continuous air barr ier the combination of interconnected materials assemblies and flexible sealed joints and
components of the building envelope that provide air-tightness
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EMC80 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 80 RH at 20C (68F)
EMC90 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 90 RH at 20C (68F)
fi ber saturation the stage in wetting and drying of wood at which the cell walls are saturated and the cell cavities
are free from water
Low-slope roof roof with a slope of less than 1 in 6 or 12deg
Moisture Design Reference Years the 10th-percentile warmest and 10th-percentile coldest years from a 30-year
weather analysisB-3
residential pertaining to single-family or multi-family dwellings including high-rise residential buildings and
manufactured homes
rain runoff the rainwater contribution that is drained from building elements above the element under consideration
Steep-slope roof roof with a slope equal to or greater than 1 in 6 or 12deg
sur face relati ve humidi ty the equilibrium relative humidity of air in contact with a surface of a given moisture
content
water-resistive barr ier a continuous material layer other than the exterior surface within a wall assembly the
purpose of which is to resist the inward migration of liquid water
32 Abbreviations and Symbols
c = 136 times 105 m2s2 (107 inHgft3lb)
F D = rain deposition factor
F E = rain exposure factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
g = gravitational acceleration constant 981 ms2 (322 fts2) H = height of the building m (ft)
m = design moisture generation rate kgs (lbh)
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (inHg)
Δ P s
= design stack pressure Pa (in of water)
Q = ventilation rate m3s (cfm)
r h = rainfall intensity on a horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) [lb(ft2h)]
T i = indoor temperature ordmC or K (ordmF or ordmR)
T o = outdoor temperature ordmC or K (ordmF or ordmR)
T o24h = 24-hour running average outdoor temperature ordmC (ordmF)
T odaily = daily average outdoor temperature ordmC (ordmF)
U = hourly average wind speed at 10 m above ground level ms (mph)
V = building volume m3 (ft3)
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wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis kgkg (lblb)
= density of outdoor air kgm3 (lbft3)
= angle between wind direction and normal to the wall (see Figure 461)
4 CRITERIA FOR DESIGN PARAMETERS
This section provides criteria for selecting design values for initial moisture conditions indoor
temperatures indoor humidity air pressure air flows weather data and rain loads
41 Design Initial Moisture ConditionsContent of Building Materials
The initial moisture content of construction materials in new construction to be used in calculations for this
standard shall be two times EMC90 for concrete and two times EMC80 for all other materials unless procedures to
dry construction materials andor procedures to protect construction materials and assemblies from wetting during
construction are specified in which case EMC90 for concrete and EMC80 for all other materials shall be used In
retrofit applications EMC90 for concrete and EMC80 for all other materials shall be used unless measured
moisture content values are availableB-4
42 Indoor Design TemperatureIf the design or operating specifications for the building specify indoor operating temperatures or the
indoor design temperatures are specified by applicable code regulation or law these temperatures shall be used
Otherwise the indoor temperatures specified in Table 42 shall be used B-5
TABLE 42 Indoor Design Temperature24-hour running average of
outdoor temperature
Indoor Design Temperature degC (degF)
Heating only Heating and air-conditioning
To 24h le 183degC
(To 24h le 65degF)
211degC
(70degF)
211 degC
(70degF)
183degC lt To 24h le 211degC
(65degF lt To 24h le 70degF)
To 24h + 28degC
(To 24h+5degF)
To 24h + 28degC
(To 24h+5degF)
To 24hgt211degC (70degF)
(To 24hgt70degF)
To 24h + 28degC
(To 24h+5degF)
239degC
(75degF)
Note To 24h = 24-hour average outdoor temperature
43 Indoor Design Humidity
If the HVAC equipment and controls are included in the design the intended design indoor humidity shall
be used If no such provisions are made then indoor design humidity shall be determined by one of three methods(a) Simplified Method (in accordance with Section 431)
(b) Intermediate Method (in accordance with Section 432) or
(c) Full Parameter Calculation (in accordance with Section 433)
The indoor design humidity shall be checked for compliance with applicable standards such asANSIASHRAE Standard 551 If calculated design humidity is outside the ranges specified measures shall be
taken to bring the humidity within the specified range
431 Indoor Design Humidity Simplified Method
Design indoor humidity according to the simplified method is a function of average daily outdoor
temperature and is given in Table 431 (Figure 431) B-6
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Table 431 Design indoor RH Simplified Method
Note To daily = Daily average outdoor temperature
- 20 - 10 0 10 20 30 20
30
40
50
60
70
80
I n d o o r D e s i g n R H [ ]
Daily Average Outdoor Temperature [degC]
68
Daily Average Outdoor Temperature [degF]
14
Figure 431 Design indoor relative humidity Simplified Method
432 Indoor Design Humidity Intermediate Method In this method indoor design humidity is determined
from hourly weather and depends on the season (Section 42) and the type of HVAC equipment
4321 Indoor Design Humidity without Dehumidification or Air-conditioning This section applies during
heating and temperature ldquofloatrdquo conditions as determined in Section 42 when cooling and dehumidification
equipment is not present or not operating Indoor vapor pressure for moisture design purposes shall be determined
using the following mass balance equation B-7
Q
mc p p h oi
24
(4-1)
where
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (in Hg)
c = 136 times 105 Pamiddotm3kg (107 inHgmiddotft3lb)
m = design moisture generation rate kgs (lbh) (in accordance with Sections 43211 and 2)
Q = design ventilation rate m3s (cfm) (in accordance with Sections 43213 and 4)
Daily Average
Outdoor Temperature
degC
Design RH
(Based on degC)
Daily Average
Outdoor Temperature
degF
Design RH
(Based on degF)
Below -10degC 40 Below 14degF 40
-10degCle To dailyle 20degC 40 + (To daily+10) 14degFle To dailyle 68degF 40 + (To daily-14)18Above 20degC 70 Above 68degF 70
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43211 Residential Moisture Generation Design values for residential moisture generation
m are based
on the expected number of occupants For design purposes a minimum of two occupants is assumed with an
additional occupant for each bedroom in addition to the master bedroom Design moisture generation rates are
given in Table 432 B-8
Table 432 Residential design moisture generation rates Number of
Bedrooms Number of Occupants
Moisture generation rate
1 bedroom 2 8 Lday 09 x 10-4 kgs 07 lbh
2 bedrooms 3 12 Lday 14 x 10-4 kgs 11 lbh
3 bedrooms 4 14 Lday 16 x 10-4 kgs 13 lbh
4 bedrooms 5 15 Lday 17 x 10-4 kgs 14 lbh
Additional bedrooms +1 per bedroom +1 Lday +01 x 10-4 kgs +01 lbh
If the home contains a jetted tub installed in a room without an automatically controlled (eg humidistat) exhaust
fan add 13 Lday or 015 x 10-4 kgs (012 lbh)
43212 Moisture Generation for Other Occupancies For other occupancies moisture generationdesign values shall be appropriate for the intended use of the building If the appropriate moisture generation rates
are not available for the intended use the simplified method (Section 431) shall be used
43213 Designed Ventilation Design ventilation rates shall be used for the calculation of design indoor
vapor pressure (Equation 4-1) The design ventilation rate to be used is the expected continuous ventilation rate
For intermittent ventilation systems ventilation effectiveness shall be accounted for according to ANSIASHRAE
Standard 6222
43214 Non-Designed Ventilation In buildings without a designed ventilation system the following
default ventilation rates shall be used for purposes of calculating the design indoor vapor pressure (Equation 4-1)
B-9
New buildings standard construction air exchange rate of 02 ach
Q = 56 x 10-5 V m3 s (4-2a)
where V is the building volume (m3) or
Q = 00033V cfm (4-2b)
where V is the building volume (ft3)
New buildings airtight construction air exchange rate of 01 ach
Q = 28 x 10-5
V m3
s (4-3a)
where V is the building volume (m3) or
Q = 00017V cfm (4-3b)
where V is building volume (ft3)
4322 Indoor Design Humidity with Air-Conditioning If the air-conditioning equipment is running and is
controlled solely by thermostat the design indoor humidity shall be derived from the following equation
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wi= 0004+04w0 (4-4)
where
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis
kgkg (lblb) B-10
If the building is air-conditioned with humidity-controlled equipment the indoor humidity design
conditions shall be the specified humidity control setting or the humidity calculated with Equation 4-4 whichever
is lower If no humidity control setting is specified the control setting shall be 50 RH
4323 Indoor Design Humidity with Dehumidification without Air-Conditioning If the building is designed
to be dehumidified with humidity-controlled dehumidification equipment and cooling equipment is not present or
not operating the indoor design humidity shall be the humidity control setting or the humidity calculated with
Equation 4-1 whichever is lower If no humidity control setting is specified the control setting shall be 50 RH
433 Indoor Design Humidity Full Parametric Calculation Full parametric evaluation of indoor humidity
requires comprehensive inputs to support the analysis of the hygrothermal response and dynamic hygrothermal
flux contribution of building elements finishes and furniture (hygric buffering) The analysis shall include thermaland mass balances and shall use simulation algorithms and time-step intervals that capture hygrothermal response
of sensitive materials and conditions
Required inputs include(a) hygrothermal properties of building materials finishes and furniture
(b) design initial moisture conditions (in accordance with Section 41)
(c) design indoor temperatures (in accordance with Section 42)
(d) design ventilation rates (in accordance with Section 43213 or 43214)
(e) design moisture generation rates (in accordance with Section 43211 or 43212)
(f) effect of active dehumidification systems
(g) design pressure data (in accordance with Section 441)
(h) design weather data (in accordance with Section 45)(i) design rain loads (in accordance with Section 46)
44 Design Air Pressure Differentials and Flows
Analysis of the effect of air pressure differentials and air flows is optional If the effect is not considered in
the design analysis this shall be expressly stated in the report If the effect is included Section 441 shall apply
441 Effect of Air Pressure Differentials Included in Design Analysis If the indoor air pressure differential
between indoors and outdoors is controlled that air pressure differential shall be used in the design analysis B-11
If the indoor air pressure differential is not managed one of two alternative procedures shall be followed
4411 Design Air Pressure Differential Alternative 1 The design air pressure differential shall be calculated
from design ventilation rates including the planned fresh air supply and exhaust rates the building air tightnesswind pressures using Moisture Design Weather Data (Section 45) and stack pressure (Section 4413)
4412 Design Air Pressure Differential Alternative 2 A design indoor air pressure differential of +5 Pa (002
in wc) above outdoor air pressure (air flow to the exterior) shall be assumed used when the 24-hour running
average outdoor temperature is below the indoor design temperatureduring the heating season and ndash 5 Pa (air flow
to the interior) when the 24-hour running average outdoor temperature is above the indoor design temperature
during the cooling season B-12
Stack pressure differential at the top of the wall of the top floor shall be calculated (Section 4413) for buildings
taller than three stories and used as the design indoor pressure differential if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
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4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
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(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 3 of 24
(This foreword is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
FOREWORD Although the majority of new buildings are safe comfortable and designed to provide effective protection
against moisture-related problems there are a certain number of buildings built each year that do experiencemoisture or mold problems Whether this number is now increasing and whether the increase is due to the greater emphasis on energy-efficiency measures today is a widely debated topic This standard is not concerned to answer
either of these questions but to provide guidance on how to best design buildings with adequate moisture control
features Given its position as a leader in the proper design of heating ventilating and air conditioning
equipment ASHRAE is uniquely qualified to provide such guidance
During the last two decades a number of computer simulation tools were developed to predict thermal
and moisture conditions in buildings and the building envelope In addition to their use as forensic tools in the
investigation of building failures these computer models are increasingly used to make recommendations for
building design in various climates However results obtained with these models are extremely sensitive to the
assumed moisture boundary conditions For instance during winter in cold climates the moisture conditions in
walls depend greatly on the indoor humidity conditions Thus a consistent approach to moisture design demands a
consistent framework for design assumptions or assumed ldquoloadsrdquo The question whether or not design features such as vapor retarders or ventilation systems are necessary cannot be answered objectively unless there is a
consensus definition of the interior and exterior moisture boundary conditions that the building is expected to be
able to sustain without negative consequences to itself or its inhabitants This standard formulates design
assumptions for moisture design analysis and criteria for acceptable performance
Ideally a design analysis involves the determination of the probability of failure treating all design
parameters and loads as stochastic variables However sufficient data are often not available to make a full
statistical treatment practical Instead a moisture design protocol will have to be based on a combination of
statistical data and professional judgment where only limited data exist Another judgment involves the choice of
an acceptable probability of the occurrence of damage Although it is common to impose very stringent criteria for
structural design because of safety concerns moisture damage usually occurs over a long period of time and
usually has less catastrophic although sometimes costly consequences An international consensus has emerged
that the analysis should be predicated on loads that will not be exceeded 90 of the time This standard hasadopted this approach
In a moisture analysis for building envelope design the choice of indoor environmental conditions is
extremely important especially for buildings in cold climates This standard opts for a design indoor climate
definition that is based on engineering principles is independent of construction and reflects the influence of
ventilation and air-conditioning equipment and controls that may or may not be part of the building design In
buildings where indoor humidity and temperature are explicitly controlled the building envelope performance
should be evaluated with the intended indoor design conditions In residential buildings indoor humidity is rarely
explicitly controlled and default design assumptions are needed for these buildings In general the standard
encourages designers to use their own design parameter values if they are known and part of the design If they
are unknown or not included in the design the standard provides default values for those loads and parameters
The standard does not address design details that deal with rainwater intrusion plumbing leaks ground
water and water damage caused by natural disasters such as floods and hurricanes While proper design for suchevents is extremely important and damage from such events involves a large percentage of moisture damage in
buildings these issues can be more effectively addressed by codes training of the trades and specific design
guidelines (see Commentary) This standard assumes that appropriate measures have been taken to limit bulk
water entry into the building and building envelope The standard does not intend to replace the judgment of the
design professional Rather it provides a framework for the design professional to identify and consider factors
that are important to the durability and serviceability of the building In addition many items in this standard are
based on incomplete information and are therefore partially based on the best professional judgment of the
standard committee at the time of writing this standard The development of this standard has pointed to many
unanswered questions questions that will hopefully be addressed and answered by research in the near future
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 4 of 24
Note to Reviewers This second publ ic review draf t makes independent substant ive changes to the fi rst
publi c review draft These changes are indicated in the text by underl in ing (for additi ons) and
str ikethrough (for deletions) Only these changes to the previous draft are open for review and
comment at th is time Additional material i s provided for context only and is not open f or comment
except as it relates to the proposed substantive changes
1 PURPOSE
The purpose of this standard is to specify performance-based design criteria for predicting mitigating or
reducing moisture damage to the building envelope materials components systems and furnishings depending on
climate construction type and HVAC system operation These criteria include
(a) criteria for selecting analytic procedures
(b) criteria for inputs and
(c) criteria for evaluation and use of outputs
2 SCOPE
21 This standard applies to the design of new buildings and to the retrofit and renovation of existing
buildings
22 This standard applies to all types of buildings building components and materials
23 This standard applies to all interior and exterior zones and building envelope cavities B-1
24 This standard does not directly apply to thermal comfort or acceptable indoor air quality B-1
25 This standard does not address the design of building components or envelopes to resist liquid water
leakage from sources such as rainwater ground water flooding or ice damsB-1
Note All superscript notes such as B-1 B-2 and so forth refer to commentary on the standard that is
contained in Informative Annex B
3 DEFINITIONS ABBREVIATIONS AND SYMBOLS
31 Definitions
24-hour r unn ing average a continuously updated average of values over the most recent 24 hours
7-day runn ing average a continuously updated average of values over the most recent 7 days
30-day running average a continuously updated average of values over the most recent 30 days
air tight construction construction in which the building envelope is designed with a continuous air barrier flow
retarder systemB-2
as-built the condition of a building assembly in a completed structure that accounts for an expected level of
deviation from the ideal construction of that assembly to address construction tolerances discontinuities and
minor defects
continuous air barr ier the combination of interconnected materials assemblies and flexible sealed joints and
components of the building envelope that provide air-tightness
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 5 of 24
EMC80 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 80 RH at 20C (68F)
EMC90 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 90 RH at 20C (68F)
fi ber saturation the stage in wetting and drying of wood at which the cell walls are saturated and the cell cavities
are free from water
Low-slope roof roof with a slope of less than 1 in 6 or 12deg
Moisture Design Reference Years the 10th-percentile warmest and 10th-percentile coldest years from a 30-year
weather analysisB-3
residential pertaining to single-family or multi-family dwellings including high-rise residential buildings and
manufactured homes
rain runoff the rainwater contribution that is drained from building elements above the element under consideration
Steep-slope roof roof with a slope equal to or greater than 1 in 6 or 12deg
sur face relati ve humidi ty the equilibrium relative humidity of air in contact with a surface of a given moisture
content
water-resistive barr ier a continuous material layer other than the exterior surface within a wall assembly the
purpose of which is to resist the inward migration of liquid water
32 Abbreviations and Symbols
c = 136 times 105 m2s2 (107 inHgft3lb)
F D = rain deposition factor
F E = rain exposure factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
g = gravitational acceleration constant 981 ms2 (322 fts2) H = height of the building m (ft)
m = design moisture generation rate kgs (lbh)
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (inHg)
Δ P s
= design stack pressure Pa (in of water)
Q = ventilation rate m3s (cfm)
r h = rainfall intensity on a horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) [lb(ft2h)]
T i = indoor temperature ordmC or K (ordmF or ordmR)
T o = outdoor temperature ordmC or K (ordmF or ordmR)
T o24h = 24-hour running average outdoor temperature ordmC (ordmF)
T odaily = daily average outdoor temperature ordmC (ordmF)
U = hourly average wind speed at 10 m above ground level ms (mph)
V = building volume m3 (ft3)
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wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis kgkg (lblb)
= density of outdoor air kgm3 (lbft3)
= angle between wind direction and normal to the wall (see Figure 461)
4 CRITERIA FOR DESIGN PARAMETERS
This section provides criteria for selecting design values for initial moisture conditions indoor
temperatures indoor humidity air pressure air flows weather data and rain loads
41 Design Initial Moisture ConditionsContent of Building Materials
The initial moisture content of construction materials in new construction to be used in calculations for this
standard shall be two times EMC90 for concrete and two times EMC80 for all other materials unless procedures to
dry construction materials andor procedures to protect construction materials and assemblies from wetting during
construction are specified in which case EMC90 for concrete and EMC80 for all other materials shall be used In
retrofit applications EMC90 for concrete and EMC80 for all other materials shall be used unless measured
moisture content values are availableB-4
42 Indoor Design TemperatureIf the design or operating specifications for the building specify indoor operating temperatures or the
indoor design temperatures are specified by applicable code regulation or law these temperatures shall be used
Otherwise the indoor temperatures specified in Table 42 shall be used B-5
TABLE 42 Indoor Design Temperature24-hour running average of
outdoor temperature
Indoor Design Temperature degC (degF)
Heating only Heating and air-conditioning
To 24h le 183degC
(To 24h le 65degF)
211degC
(70degF)
211 degC
(70degF)
183degC lt To 24h le 211degC
(65degF lt To 24h le 70degF)
To 24h + 28degC
(To 24h+5degF)
To 24h + 28degC
(To 24h+5degF)
To 24hgt211degC (70degF)
(To 24hgt70degF)
To 24h + 28degC
(To 24h+5degF)
239degC
(75degF)
Note To 24h = 24-hour average outdoor temperature
43 Indoor Design Humidity
If the HVAC equipment and controls are included in the design the intended design indoor humidity shall
be used If no such provisions are made then indoor design humidity shall be determined by one of three methods(a) Simplified Method (in accordance with Section 431)
(b) Intermediate Method (in accordance with Section 432) or
(c) Full Parameter Calculation (in accordance with Section 433)
The indoor design humidity shall be checked for compliance with applicable standards such asANSIASHRAE Standard 551 If calculated design humidity is outside the ranges specified measures shall be
taken to bring the humidity within the specified range
431 Indoor Design Humidity Simplified Method
Design indoor humidity according to the simplified method is a function of average daily outdoor
temperature and is given in Table 431 (Figure 431) B-6
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Table 431 Design indoor RH Simplified Method
Note To daily = Daily average outdoor temperature
- 20 - 10 0 10 20 30 20
30
40
50
60
70
80
I n d o o r D e s i g n R H [ ]
Daily Average Outdoor Temperature [degC]
68
Daily Average Outdoor Temperature [degF]
14
Figure 431 Design indoor relative humidity Simplified Method
432 Indoor Design Humidity Intermediate Method In this method indoor design humidity is determined
from hourly weather and depends on the season (Section 42) and the type of HVAC equipment
4321 Indoor Design Humidity without Dehumidification or Air-conditioning This section applies during
heating and temperature ldquofloatrdquo conditions as determined in Section 42 when cooling and dehumidification
equipment is not present or not operating Indoor vapor pressure for moisture design purposes shall be determined
using the following mass balance equation B-7
Q
mc p p h oi
24
(4-1)
where
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (in Hg)
c = 136 times 105 Pamiddotm3kg (107 inHgmiddotft3lb)
m = design moisture generation rate kgs (lbh) (in accordance with Sections 43211 and 2)
Q = design ventilation rate m3s (cfm) (in accordance with Sections 43213 and 4)
Daily Average
Outdoor Temperature
degC
Design RH
(Based on degC)
Daily Average
Outdoor Temperature
degF
Design RH
(Based on degF)
Below -10degC 40 Below 14degF 40
-10degCle To dailyle 20degC 40 + (To daily+10) 14degFle To dailyle 68degF 40 + (To daily-14)18Above 20degC 70 Above 68degF 70
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43211 Residential Moisture Generation Design values for residential moisture generation
m are based
on the expected number of occupants For design purposes a minimum of two occupants is assumed with an
additional occupant for each bedroom in addition to the master bedroom Design moisture generation rates are
given in Table 432 B-8
Table 432 Residential design moisture generation rates Number of
Bedrooms Number of Occupants
Moisture generation rate
1 bedroom 2 8 Lday 09 x 10-4 kgs 07 lbh
2 bedrooms 3 12 Lday 14 x 10-4 kgs 11 lbh
3 bedrooms 4 14 Lday 16 x 10-4 kgs 13 lbh
4 bedrooms 5 15 Lday 17 x 10-4 kgs 14 lbh
Additional bedrooms +1 per bedroom +1 Lday +01 x 10-4 kgs +01 lbh
If the home contains a jetted tub installed in a room without an automatically controlled (eg humidistat) exhaust
fan add 13 Lday or 015 x 10-4 kgs (012 lbh)
43212 Moisture Generation for Other Occupancies For other occupancies moisture generationdesign values shall be appropriate for the intended use of the building If the appropriate moisture generation rates
are not available for the intended use the simplified method (Section 431) shall be used
43213 Designed Ventilation Design ventilation rates shall be used for the calculation of design indoor
vapor pressure (Equation 4-1) The design ventilation rate to be used is the expected continuous ventilation rate
For intermittent ventilation systems ventilation effectiveness shall be accounted for according to ANSIASHRAE
Standard 6222
43214 Non-Designed Ventilation In buildings without a designed ventilation system the following
default ventilation rates shall be used for purposes of calculating the design indoor vapor pressure (Equation 4-1)
B-9
New buildings standard construction air exchange rate of 02 ach
Q = 56 x 10-5 V m3 s (4-2a)
where V is the building volume (m3) or
Q = 00033V cfm (4-2b)
where V is the building volume (ft3)
New buildings airtight construction air exchange rate of 01 ach
Q = 28 x 10-5
V m3
s (4-3a)
where V is the building volume (m3) or
Q = 00017V cfm (4-3b)
where V is building volume (ft3)
4322 Indoor Design Humidity with Air-Conditioning If the air-conditioning equipment is running and is
controlled solely by thermostat the design indoor humidity shall be derived from the following equation
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wi= 0004+04w0 (4-4)
where
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis
kgkg (lblb) B-10
If the building is air-conditioned with humidity-controlled equipment the indoor humidity design
conditions shall be the specified humidity control setting or the humidity calculated with Equation 4-4 whichever
is lower If no humidity control setting is specified the control setting shall be 50 RH
4323 Indoor Design Humidity with Dehumidification without Air-Conditioning If the building is designed
to be dehumidified with humidity-controlled dehumidification equipment and cooling equipment is not present or
not operating the indoor design humidity shall be the humidity control setting or the humidity calculated with
Equation 4-1 whichever is lower If no humidity control setting is specified the control setting shall be 50 RH
433 Indoor Design Humidity Full Parametric Calculation Full parametric evaluation of indoor humidity
requires comprehensive inputs to support the analysis of the hygrothermal response and dynamic hygrothermal
flux contribution of building elements finishes and furniture (hygric buffering) The analysis shall include thermaland mass balances and shall use simulation algorithms and time-step intervals that capture hygrothermal response
of sensitive materials and conditions
Required inputs include(a) hygrothermal properties of building materials finishes and furniture
(b) design initial moisture conditions (in accordance with Section 41)
(c) design indoor temperatures (in accordance with Section 42)
(d) design ventilation rates (in accordance with Section 43213 or 43214)
(e) design moisture generation rates (in accordance with Section 43211 or 43212)
(f) effect of active dehumidification systems
(g) design pressure data (in accordance with Section 441)
(h) design weather data (in accordance with Section 45)(i) design rain loads (in accordance with Section 46)
44 Design Air Pressure Differentials and Flows
Analysis of the effect of air pressure differentials and air flows is optional If the effect is not considered in
the design analysis this shall be expressly stated in the report If the effect is included Section 441 shall apply
441 Effect of Air Pressure Differentials Included in Design Analysis If the indoor air pressure differential
between indoors and outdoors is controlled that air pressure differential shall be used in the design analysis B-11
If the indoor air pressure differential is not managed one of two alternative procedures shall be followed
4411 Design Air Pressure Differential Alternative 1 The design air pressure differential shall be calculated
from design ventilation rates including the planned fresh air supply and exhaust rates the building air tightnesswind pressures using Moisture Design Weather Data (Section 45) and stack pressure (Section 4413)
4412 Design Air Pressure Differential Alternative 2 A design indoor air pressure differential of +5 Pa (002
in wc) above outdoor air pressure (air flow to the exterior) shall be assumed used when the 24-hour running
average outdoor temperature is below the indoor design temperatureduring the heating season and ndash 5 Pa (air flow
to the interior) when the 24-hour running average outdoor temperature is above the indoor design temperature
during the cooling season B-12
Stack pressure differential at the top of the wall of the top floor shall be calculated (Section 4413) for buildings
taller than three stories and used as the design indoor pressure differential if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
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Page 10 of 24
4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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Page 11 of 24
U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
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Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 4 of 24
Note to Reviewers This second publ ic review draf t makes independent substant ive changes to the fi rst
publi c review draft These changes are indicated in the text by underl in ing (for additi ons) and
str ikethrough (for deletions) Only these changes to the previous draft are open for review and
comment at th is time Additional material i s provided for context only and is not open f or comment
except as it relates to the proposed substantive changes
1 PURPOSE
The purpose of this standard is to specify performance-based design criteria for predicting mitigating or
reducing moisture damage to the building envelope materials components systems and furnishings depending on
climate construction type and HVAC system operation These criteria include
(a) criteria for selecting analytic procedures
(b) criteria for inputs and
(c) criteria for evaluation and use of outputs
2 SCOPE
21 This standard applies to the design of new buildings and to the retrofit and renovation of existing
buildings
22 This standard applies to all types of buildings building components and materials
23 This standard applies to all interior and exterior zones and building envelope cavities B-1
24 This standard does not directly apply to thermal comfort or acceptable indoor air quality B-1
25 This standard does not address the design of building components or envelopes to resist liquid water
leakage from sources such as rainwater ground water flooding or ice damsB-1
Note All superscript notes such as B-1 B-2 and so forth refer to commentary on the standard that is
contained in Informative Annex B
3 DEFINITIONS ABBREVIATIONS AND SYMBOLS
31 Definitions
24-hour r unn ing average a continuously updated average of values over the most recent 24 hours
7-day runn ing average a continuously updated average of values over the most recent 7 days
30-day running average a continuously updated average of values over the most recent 30 days
air tight construction construction in which the building envelope is designed with a continuous air barrier flow
retarder systemB-2
as-built the condition of a building assembly in a completed structure that accounts for an expected level of
deviation from the ideal construction of that assembly to address construction tolerances discontinuities and
minor defects
continuous air barr ier the combination of interconnected materials assemblies and flexible sealed joints and
components of the building envelope that provide air-tightness
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 5 of 24
EMC80 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 80 RH at 20C (68F)
EMC90 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 90 RH at 20C (68F)
fi ber saturation the stage in wetting and drying of wood at which the cell walls are saturated and the cell cavities
are free from water
Low-slope roof roof with a slope of less than 1 in 6 or 12deg
Moisture Design Reference Years the 10th-percentile warmest and 10th-percentile coldest years from a 30-year
weather analysisB-3
residential pertaining to single-family or multi-family dwellings including high-rise residential buildings and
manufactured homes
rain runoff the rainwater contribution that is drained from building elements above the element under consideration
Steep-slope roof roof with a slope equal to or greater than 1 in 6 or 12deg
sur face relati ve humidi ty the equilibrium relative humidity of air in contact with a surface of a given moisture
content
water-resistive barr ier a continuous material layer other than the exterior surface within a wall assembly the
purpose of which is to resist the inward migration of liquid water
32 Abbreviations and Symbols
c = 136 times 105 m2s2 (107 inHgft3lb)
F D = rain deposition factor
F E = rain exposure factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
g = gravitational acceleration constant 981 ms2 (322 fts2) H = height of the building m (ft)
m = design moisture generation rate kgs (lbh)
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (inHg)
Δ P s
= design stack pressure Pa (in of water)
Q = ventilation rate m3s (cfm)
r h = rainfall intensity on a horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) [lb(ft2h)]
T i = indoor temperature ordmC or K (ordmF or ordmR)
T o = outdoor temperature ordmC or K (ordmF or ordmR)
T o24h = 24-hour running average outdoor temperature ordmC (ordmF)
T odaily = daily average outdoor temperature ordmC (ordmF)
U = hourly average wind speed at 10 m above ground level ms (mph)
V = building volume m3 (ft3)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 6 of 24
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis kgkg (lblb)
= density of outdoor air kgm3 (lbft3)
= angle between wind direction and normal to the wall (see Figure 461)
4 CRITERIA FOR DESIGN PARAMETERS
This section provides criteria for selecting design values for initial moisture conditions indoor
temperatures indoor humidity air pressure air flows weather data and rain loads
41 Design Initial Moisture ConditionsContent of Building Materials
The initial moisture content of construction materials in new construction to be used in calculations for this
standard shall be two times EMC90 for concrete and two times EMC80 for all other materials unless procedures to
dry construction materials andor procedures to protect construction materials and assemblies from wetting during
construction are specified in which case EMC90 for concrete and EMC80 for all other materials shall be used In
retrofit applications EMC90 for concrete and EMC80 for all other materials shall be used unless measured
moisture content values are availableB-4
42 Indoor Design TemperatureIf the design or operating specifications for the building specify indoor operating temperatures or the
indoor design temperatures are specified by applicable code regulation or law these temperatures shall be used
Otherwise the indoor temperatures specified in Table 42 shall be used B-5
TABLE 42 Indoor Design Temperature24-hour running average of
outdoor temperature
Indoor Design Temperature degC (degF)
Heating only Heating and air-conditioning
To 24h le 183degC
(To 24h le 65degF)
211degC
(70degF)
211 degC
(70degF)
183degC lt To 24h le 211degC
(65degF lt To 24h le 70degF)
To 24h + 28degC
(To 24h+5degF)
To 24h + 28degC
(To 24h+5degF)
To 24hgt211degC (70degF)
(To 24hgt70degF)
To 24h + 28degC
(To 24h+5degF)
239degC
(75degF)
Note To 24h = 24-hour average outdoor temperature
43 Indoor Design Humidity
If the HVAC equipment and controls are included in the design the intended design indoor humidity shall
be used If no such provisions are made then indoor design humidity shall be determined by one of three methods(a) Simplified Method (in accordance with Section 431)
(b) Intermediate Method (in accordance with Section 432) or
(c) Full Parameter Calculation (in accordance with Section 433)
The indoor design humidity shall be checked for compliance with applicable standards such asANSIASHRAE Standard 551 If calculated design humidity is outside the ranges specified measures shall be
taken to bring the humidity within the specified range
431 Indoor Design Humidity Simplified Method
Design indoor humidity according to the simplified method is a function of average daily outdoor
temperature and is given in Table 431 (Figure 431) B-6
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 7 of 24
Table 431 Design indoor RH Simplified Method
Note To daily = Daily average outdoor temperature
- 20 - 10 0 10 20 30 20
30
40
50
60
70
80
I n d o o r D e s i g n R H [ ]
Daily Average Outdoor Temperature [degC]
68
Daily Average Outdoor Temperature [degF]
14
Figure 431 Design indoor relative humidity Simplified Method
432 Indoor Design Humidity Intermediate Method In this method indoor design humidity is determined
from hourly weather and depends on the season (Section 42) and the type of HVAC equipment
4321 Indoor Design Humidity without Dehumidification or Air-conditioning This section applies during
heating and temperature ldquofloatrdquo conditions as determined in Section 42 when cooling and dehumidification
equipment is not present or not operating Indoor vapor pressure for moisture design purposes shall be determined
using the following mass balance equation B-7
Q
mc p p h oi
24
(4-1)
where
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (in Hg)
c = 136 times 105 Pamiddotm3kg (107 inHgmiddotft3lb)
m = design moisture generation rate kgs (lbh) (in accordance with Sections 43211 and 2)
Q = design ventilation rate m3s (cfm) (in accordance with Sections 43213 and 4)
Daily Average
Outdoor Temperature
degC
Design RH
(Based on degC)
Daily Average
Outdoor Temperature
degF
Design RH
(Based on degF)
Below -10degC 40 Below 14degF 40
-10degCle To dailyle 20degC 40 + (To daily+10) 14degFle To dailyle 68degF 40 + (To daily-14)18Above 20degC 70 Above 68degF 70
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 8 of 24
43211 Residential Moisture Generation Design values for residential moisture generation
m are based
on the expected number of occupants For design purposes a minimum of two occupants is assumed with an
additional occupant for each bedroom in addition to the master bedroom Design moisture generation rates are
given in Table 432 B-8
Table 432 Residential design moisture generation rates Number of
Bedrooms Number of Occupants
Moisture generation rate
1 bedroom 2 8 Lday 09 x 10-4 kgs 07 lbh
2 bedrooms 3 12 Lday 14 x 10-4 kgs 11 lbh
3 bedrooms 4 14 Lday 16 x 10-4 kgs 13 lbh
4 bedrooms 5 15 Lday 17 x 10-4 kgs 14 lbh
Additional bedrooms +1 per bedroom +1 Lday +01 x 10-4 kgs +01 lbh
If the home contains a jetted tub installed in a room without an automatically controlled (eg humidistat) exhaust
fan add 13 Lday or 015 x 10-4 kgs (012 lbh)
43212 Moisture Generation for Other Occupancies For other occupancies moisture generationdesign values shall be appropriate for the intended use of the building If the appropriate moisture generation rates
are not available for the intended use the simplified method (Section 431) shall be used
43213 Designed Ventilation Design ventilation rates shall be used for the calculation of design indoor
vapor pressure (Equation 4-1) The design ventilation rate to be used is the expected continuous ventilation rate
For intermittent ventilation systems ventilation effectiveness shall be accounted for according to ANSIASHRAE
Standard 6222
43214 Non-Designed Ventilation In buildings without a designed ventilation system the following
default ventilation rates shall be used for purposes of calculating the design indoor vapor pressure (Equation 4-1)
B-9
New buildings standard construction air exchange rate of 02 ach
Q = 56 x 10-5 V m3 s (4-2a)
where V is the building volume (m3) or
Q = 00033V cfm (4-2b)
where V is the building volume (ft3)
New buildings airtight construction air exchange rate of 01 ach
Q = 28 x 10-5
V m3
s (4-3a)
where V is the building volume (m3) or
Q = 00017V cfm (4-3b)
where V is building volume (ft3)
4322 Indoor Design Humidity with Air-Conditioning If the air-conditioning equipment is running and is
controlled solely by thermostat the design indoor humidity shall be derived from the following equation
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 9 of 24
wi= 0004+04w0 (4-4)
where
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis
kgkg (lblb) B-10
If the building is air-conditioned with humidity-controlled equipment the indoor humidity design
conditions shall be the specified humidity control setting or the humidity calculated with Equation 4-4 whichever
is lower If no humidity control setting is specified the control setting shall be 50 RH
4323 Indoor Design Humidity with Dehumidification without Air-Conditioning If the building is designed
to be dehumidified with humidity-controlled dehumidification equipment and cooling equipment is not present or
not operating the indoor design humidity shall be the humidity control setting or the humidity calculated with
Equation 4-1 whichever is lower If no humidity control setting is specified the control setting shall be 50 RH
433 Indoor Design Humidity Full Parametric Calculation Full parametric evaluation of indoor humidity
requires comprehensive inputs to support the analysis of the hygrothermal response and dynamic hygrothermal
flux contribution of building elements finishes and furniture (hygric buffering) The analysis shall include thermaland mass balances and shall use simulation algorithms and time-step intervals that capture hygrothermal response
of sensitive materials and conditions
Required inputs include(a) hygrothermal properties of building materials finishes and furniture
(b) design initial moisture conditions (in accordance with Section 41)
(c) design indoor temperatures (in accordance with Section 42)
(d) design ventilation rates (in accordance with Section 43213 or 43214)
(e) design moisture generation rates (in accordance with Section 43211 or 43212)
(f) effect of active dehumidification systems
(g) design pressure data (in accordance with Section 441)
(h) design weather data (in accordance with Section 45)(i) design rain loads (in accordance with Section 46)
44 Design Air Pressure Differentials and Flows
Analysis of the effect of air pressure differentials and air flows is optional If the effect is not considered in
the design analysis this shall be expressly stated in the report If the effect is included Section 441 shall apply
441 Effect of Air Pressure Differentials Included in Design Analysis If the indoor air pressure differential
between indoors and outdoors is controlled that air pressure differential shall be used in the design analysis B-11
If the indoor air pressure differential is not managed one of two alternative procedures shall be followed
4411 Design Air Pressure Differential Alternative 1 The design air pressure differential shall be calculated
from design ventilation rates including the planned fresh air supply and exhaust rates the building air tightnesswind pressures using Moisture Design Weather Data (Section 45) and stack pressure (Section 4413)
4412 Design Air Pressure Differential Alternative 2 A design indoor air pressure differential of +5 Pa (002
in wc) above outdoor air pressure (air flow to the exterior) shall be assumed used when the 24-hour running
average outdoor temperature is below the indoor design temperatureduring the heating season and ndash 5 Pa (air flow
to the interior) when the 24-hour running average outdoor temperature is above the indoor design temperature
during the cooling season B-12
Stack pressure differential at the top of the wall of the top floor shall be calculated (Section 4413) for buildings
taller than three stories and used as the design indoor pressure differential if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 10 of 24
4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 11 of 24
U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 5 of 24
EMC80 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 80 RH at 20C (68F)
EMC90 the moisture content of a material expressed as a ratio of the mass of water and the oven-dry mass when
the material is in equilibrium with air at 90 RH at 20C (68F)
fi ber saturation the stage in wetting and drying of wood at which the cell walls are saturated and the cell cavities
are free from water
Low-slope roof roof with a slope of less than 1 in 6 or 12deg
Moisture Design Reference Years the 10th-percentile warmest and 10th-percentile coldest years from a 30-year
weather analysisB-3
residential pertaining to single-family or multi-family dwellings including high-rise residential buildings and
manufactured homes
rain runoff the rainwater contribution that is drained from building elements above the element under consideration
Steep-slope roof roof with a slope equal to or greater than 1 in 6 or 12deg
sur face relati ve humidi ty the equilibrium relative humidity of air in contact with a surface of a given moisture
content
water-resistive barr ier a continuous material layer other than the exterior surface within a wall assembly the
purpose of which is to resist the inward migration of liquid water
32 Abbreviations and Symbols
c = 136 times 105 m2s2 (107 inHgft3lb)
F D = rain deposition factor
F E = rain exposure factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
g = gravitational acceleration constant 981 ms2 (322 fts2) H = height of the building m (ft)
m = design moisture generation rate kgs (lbh)
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (inHg)
Δ P s
= design stack pressure Pa (in of water)
Q = ventilation rate m3s (cfm)
r h = rainfall intensity on a horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) [lb(ft2h)]
T i = indoor temperature ordmC or K (ordmF or ordmR)
T o = outdoor temperature ordmC or K (ordmF or ordmR)
T o24h = 24-hour running average outdoor temperature ordmC (ordmF)
T odaily = daily average outdoor temperature ordmC (ordmF)
U = hourly average wind speed at 10 m above ground level ms (mph)
V = building volume m3 (ft3)
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Page 6 of 24
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis kgkg (lblb)
= density of outdoor air kgm3 (lbft3)
= angle between wind direction and normal to the wall (see Figure 461)
4 CRITERIA FOR DESIGN PARAMETERS
This section provides criteria for selecting design values for initial moisture conditions indoor
temperatures indoor humidity air pressure air flows weather data and rain loads
41 Design Initial Moisture ConditionsContent of Building Materials
The initial moisture content of construction materials in new construction to be used in calculations for this
standard shall be two times EMC90 for concrete and two times EMC80 for all other materials unless procedures to
dry construction materials andor procedures to protect construction materials and assemblies from wetting during
construction are specified in which case EMC90 for concrete and EMC80 for all other materials shall be used In
retrofit applications EMC90 for concrete and EMC80 for all other materials shall be used unless measured
moisture content values are availableB-4
42 Indoor Design TemperatureIf the design or operating specifications for the building specify indoor operating temperatures or the
indoor design temperatures are specified by applicable code regulation or law these temperatures shall be used
Otherwise the indoor temperatures specified in Table 42 shall be used B-5
TABLE 42 Indoor Design Temperature24-hour running average of
outdoor temperature
Indoor Design Temperature degC (degF)
Heating only Heating and air-conditioning
To 24h le 183degC
(To 24h le 65degF)
211degC
(70degF)
211 degC
(70degF)
183degC lt To 24h le 211degC
(65degF lt To 24h le 70degF)
To 24h + 28degC
(To 24h+5degF)
To 24h + 28degC
(To 24h+5degF)
To 24hgt211degC (70degF)
(To 24hgt70degF)
To 24h + 28degC
(To 24h+5degF)
239degC
(75degF)
Note To 24h = 24-hour average outdoor temperature
43 Indoor Design Humidity
If the HVAC equipment and controls are included in the design the intended design indoor humidity shall
be used If no such provisions are made then indoor design humidity shall be determined by one of three methods(a) Simplified Method (in accordance with Section 431)
(b) Intermediate Method (in accordance with Section 432) or
(c) Full Parameter Calculation (in accordance with Section 433)
The indoor design humidity shall be checked for compliance with applicable standards such asANSIASHRAE Standard 551 If calculated design humidity is outside the ranges specified measures shall be
taken to bring the humidity within the specified range
431 Indoor Design Humidity Simplified Method
Design indoor humidity according to the simplified method is a function of average daily outdoor
temperature and is given in Table 431 (Figure 431) B-6
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
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Page 7 of 24
Table 431 Design indoor RH Simplified Method
Note To daily = Daily average outdoor temperature
- 20 - 10 0 10 20 30 20
30
40
50
60
70
80
I n d o o r D e s i g n R H [ ]
Daily Average Outdoor Temperature [degC]
68
Daily Average Outdoor Temperature [degF]
14
Figure 431 Design indoor relative humidity Simplified Method
432 Indoor Design Humidity Intermediate Method In this method indoor design humidity is determined
from hourly weather and depends on the season (Section 42) and the type of HVAC equipment
4321 Indoor Design Humidity without Dehumidification or Air-conditioning This section applies during
heating and temperature ldquofloatrdquo conditions as determined in Section 42 when cooling and dehumidification
equipment is not present or not operating Indoor vapor pressure for moisture design purposes shall be determined
using the following mass balance equation B-7
Q
mc p p h oi
24
(4-1)
where
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (in Hg)
c = 136 times 105 Pamiddotm3kg (107 inHgmiddotft3lb)
m = design moisture generation rate kgs (lbh) (in accordance with Sections 43211 and 2)
Q = design ventilation rate m3s (cfm) (in accordance with Sections 43213 and 4)
Daily Average
Outdoor Temperature
degC
Design RH
(Based on degC)
Daily Average
Outdoor Temperature
degF
Design RH
(Based on degF)
Below -10degC 40 Below 14degF 40
-10degCle To dailyle 20degC 40 + (To daily+10) 14degFle To dailyle 68degF 40 + (To daily-14)18Above 20degC 70 Above 68degF 70
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Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 8 of 24
43211 Residential Moisture Generation Design values for residential moisture generation
m are based
on the expected number of occupants For design purposes a minimum of two occupants is assumed with an
additional occupant for each bedroom in addition to the master bedroom Design moisture generation rates are
given in Table 432 B-8
Table 432 Residential design moisture generation rates Number of
Bedrooms Number of Occupants
Moisture generation rate
1 bedroom 2 8 Lday 09 x 10-4 kgs 07 lbh
2 bedrooms 3 12 Lday 14 x 10-4 kgs 11 lbh
3 bedrooms 4 14 Lday 16 x 10-4 kgs 13 lbh
4 bedrooms 5 15 Lday 17 x 10-4 kgs 14 lbh
Additional bedrooms +1 per bedroom +1 Lday +01 x 10-4 kgs +01 lbh
If the home contains a jetted tub installed in a room without an automatically controlled (eg humidistat) exhaust
fan add 13 Lday or 015 x 10-4 kgs (012 lbh)
43212 Moisture Generation for Other Occupancies For other occupancies moisture generationdesign values shall be appropriate for the intended use of the building If the appropriate moisture generation rates
are not available for the intended use the simplified method (Section 431) shall be used
43213 Designed Ventilation Design ventilation rates shall be used for the calculation of design indoor
vapor pressure (Equation 4-1) The design ventilation rate to be used is the expected continuous ventilation rate
For intermittent ventilation systems ventilation effectiveness shall be accounted for according to ANSIASHRAE
Standard 6222
43214 Non-Designed Ventilation In buildings without a designed ventilation system the following
default ventilation rates shall be used for purposes of calculating the design indoor vapor pressure (Equation 4-1)
B-9
New buildings standard construction air exchange rate of 02 ach
Q = 56 x 10-5 V m3 s (4-2a)
where V is the building volume (m3) or
Q = 00033V cfm (4-2b)
where V is the building volume (ft3)
New buildings airtight construction air exchange rate of 01 ach
Q = 28 x 10-5
V m3
s (4-3a)
where V is the building volume (m3) or
Q = 00017V cfm (4-3b)
where V is building volume (ft3)
4322 Indoor Design Humidity with Air-Conditioning If the air-conditioning equipment is running and is
controlled solely by thermostat the design indoor humidity shall be derived from the following equation
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 9 of 24
wi= 0004+04w0 (4-4)
where
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis
kgkg (lblb) B-10
If the building is air-conditioned with humidity-controlled equipment the indoor humidity design
conditions shall be the specified humidity control setting or the humidity calculated with Equation 4-4 whichever
is lower If no humidity control setting is specified the control setting shall be 50 RH
4323 Indoor Design Humidity with Dehumidification without Air-Conditioning If the building is designed
to be dehumidified with humidity-controlled dehumidification equipment and cooling equipment is not present or
not operating the indoor design humidity shall be the humidity control setting or the humidity calculated with
Equation 4-1 whichever is lower If no humidity control setting is specified the control setting shall be 50 RH
433 Indoor Design Humidity Full Parametric Calculation Full parametric evaluation of indoor humidity
requires comprehensive inputs to support the analysis of the hygrothermal response and dynamic hygrothermal
flux contribution of building elements finishes and furniture (hygric buffering) The analysis shall include thermaland mass balances and shall use simulation algorithms and time-step intervals that capture hygrothermal response
of sensitive materials and conditions
Required inputs include(a) hygrothermal properties of building materials finishes and furniture
(b) design initial moisture conditions (in accordance with Section 41)
(c) design indoor temperatures (in accordance with Section 42)
(d) design ventilation rates (in accordance with Section 43213 or 43214)
(e) design moisture generation rates (in accordance with Section 43211 or 43212)
(f) effect of active dehumidification systems
(g) design pressure data (in accordance with Section 441)
(h) design weather data (in accordance with Section 45)(i) design rain loads (in accordance with Section 46)
44 Design Air Pressure Differentials and Flows
Analysis of the effect of air pressure differentials and air flows is optional If the effect is not considered in
the design analysis this shall be expressly stated in the report If the effect is included Section 441 shall apply
441 Effect of Air Pressure Differentials Included in Design Analysis If the indoor air pressure differential
between indoors and outdoors is controlled that air pressure differential shall be used in the design analysis B-11
If the indoor air pressure differential is not managed one of two alternative procedures shall be followed
4411 Design Air Pressure Differential Alternative 1 The design air pressure differential shall be calculated
from design ventilation rates including the planned fresh air supply and exhaust rates the building air tightnesswind pressures using Moisture Design Weather Data (Section 45) and stack pressure (Section 4413)
4412 Design Air Pressure Differential Alternative 2 A design indoor air pressure differential of +5 Pa (002
in wc) above outdoor air pressure (air flow to the exterior) shall be assumed used when the 24-hour running
average outdoor temperature is below the indoor design temperatureduring the heating season and ndash 5 Pa (air flow
to the interior) when the 24-hour running average outdoor temperature is above the indoor design temperature
during the cooling season B-12
Stack pressure differential at the top of the wall of the top floor shall be calculated (Section 4413) for buildings
taller than three stories and used as the design indoor pressure differential if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 10 of 24
4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 11 of 24
U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 6 of 24
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis kgkg (lblb)
= density of outdoor air kgm3 (lbft3)
= angle between wind direction and normal to the wall (see Figure 461)
4 CRITERIA FOR DESIGN PARAMETERS
This section provides criteria for selecting design values for initial moisture conditions indoor
temperatures indoor humidity air pressure air flows weather data and rain loads
41 Design Initial Moisture ConditionsContent of Building Materials
The initial moisture content of construction materials in new construction to be used in calculations for this
standard shall be two times EMC90 for concrete and two times EMC80 for all other materials unless procedures to
dry construction materials andor procedures to protect construction materials and assemblies from wetting during
construction are specified in which case EMC90 for concrete and EMC80 for all other materials shall be used In
retrofit applications EMC90 for concrete and EMC80 for all other materials shall be used unless measured
moisture content values are availableB-4
42 Indoor Design TemperatureIf the design or operating specifications for the building specify indoor operating temperatures or the
indoor design temperatures are specified by applicable code regulation or law these temperatures shall be used
Otherwise the indoor temperatures specified in Table 42 shall be used B-5
TABLE 42 Indoor Design Temperature24-hour running average of
outdoor temperature
Indoor Design Temperature degC (degF)
Heating only Heating and air-conditioning
To 24h le 183degC
(To 24h le 65degF)
211degC
(70degF)
211 degC
(70degF)
183degC lt To 24h le 211degC
(65degF lt To 24h le 70degF)
To 24h + 28degC
(To 24h+5degF)
To 24h + 28degC
(To 24h+5degF)
To 24hgt211degC (70degF)
(To 24hgt70degF)
To 24h + 28degC
(To 24h+5degF)
239degC
(75degF)
Note To 24h = 24-hour average outdoor temperature
43 Indoor Design Humidity
If the HVAC equipment and controls are included in the design the intended design indoor humidity shall
be used If no such provisions are made then indoor design humidity shall be determined by one of three methods(a) Simplified Method (in accordance with Section 431)
(b) Intermediate Method (in accordance with Section 432) or
(c) Full Parameter Calculation (in accordance with Section 433)
The indoor design humidity shall be checked for compliance with applicable standards such asANSIASHRAE Standard 551 If calculated design humidity is outside the ranges specified measures shall be
taken to bring the humidity within the specified range
431 Indoor Design Humidity Simplified Method
Design indoor humidity according to the simplified method is a function of average daily outdoor
temperature and is given in Table 431 (Figure 431) B-6
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 7 of 24
Table 431 Design indoor RH Simplified Method
Note To daily = Daily average outdoor temperature
- 20 - 10 0 10 20 30 20
30
40
50
60
70
80
I n d o o r D e s i g n R H [ ]
Daily Average Outdoor Temperature [degC]
68
Daily Average Outdoor Temperature [degF]
14
Figure 431 Design indoor relative humidity Simplified Method
432 Indoor Design Humidity Intermediate Method In this method indoor design humidity is determined
from hourly weather and depends on the season (Section 42) and the type of HVAC equipment
4321 Indoor Design Humidity without Dehumidification or Air-conditioning This section applies during
heating and temperature ldquofloatrdquo conditions as determined in Section 42 when cooling and dehumidification
equipment is not present or not operating Indoor vapor pressure for moisture design purposes shall be determined
using the following mass balance equation B-7
Q
mc p p h oi
24
(4-1)
where
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (in Hg)
c = 136 times 105 Pamiddotm3kg (107 inHgmiddotft3lb)
m = design moisture generation rate kgs (lbh) (in accordance with Sections 43211 and 2)
Q = design ventilation rate m3s (cfm) (in accordance with Sections 43213 and 4)
Daily Average
Outdoor Temperature
degC
Design RH
(Based on degC)
Daily Average
Outdoor Temperature
degF
Design RH
(Based on degF)
Below -10degC 40 Below 14degF 40
-10degCle To dailyle 20degC 40 + (To daily+10) 14degFle To dailyle 68degF 40 + (To daily-14)18Above 20degC 70 Above 68degF 70
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 8 of 24
43211 Residential Moisture Generation Design values for residential moisture generation
m are based
on the expected number of occupants For design purposes a minimum of two occupants is assumed with an
additional occupant for each bedroom in addition to the master bedroom Design moisture generation rates are
given in Table 432 B-8
Table 432 Residential design moisture generation rates Number of
Bedrooms Number of Occupants
Moisture generation rate
1 bedroom 2 8 Lday 09 x 10-4 kgs 07 lbh
2 bedrooms 3 12 Lday 14 x 10-4 kgs 11 lbh
3 bedrooms 4 14 Lday 16 x 10-4 kgs 13 lbh
4 bedrooms 5 15 Lday 17 x 10-4 kgs 14 lbh
Additional bedrooms +1 per bedroom +1 Lday +01 x 10-4 kgs +01 lbh
If the home contains a jetted tub installed in a room without an automatically controlled (eg humidistat) exhaust
fan add 13 Lday or 015 x 10-4 kgs (012 lbh)
43212 Moisture Generation for Other Occupancies For other occupancies moisture generationdesign values shall be appropriate for the intended use of the building If the appropriate moisture generation rates
are not available for the intended use the simplified method (Section 431) shall be used
43213 Designed Ventilation Design ventilation rates shall be used for the calculation of design indoor
vapor pressure (Equation 4-1) The design ventilation rate to be used is the expected continuous ventilation rate
For intermittent ventilation systems ventilation effectiveness shall be accounted for according to ANSIASHRAE
Standard 6222
43214 Non-Designed Ventilation In buildings without a designed ventilation system the following
default ventilation rates shall be used for purposes of calculating the design indoor vapor pressure (Equation 4-1)
B-9
New buildings standard construction air exchange rate of 02 ach
Q = 56 x 10-5 V m3 s (4-2a)
where V is the building volume (m3) or
Q = 00033V cfm (4-2b)
where V is the building volume (ft3)
New buildings airtight construction air exchange rate of 01 ach
Q = 28 x 10-5
V m3
s (4-3a)
where V is the building volume (m3) or
Q = 00017V cfm (4-3b)
where V is building volume (ft3)
4322 Indoor Design Humidity with Air-Conditioning If the air-conditioning equipment is running and is
controlled solely by thermostat the design indoor humidity shall be derived from the following equation
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 9 of 24
wi= 0004+04w0 (4-4)
where
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis
kgkg (lblb) B-10
If the building is air-conditioned with humidity-controlled equipment the indoor humidity design
conditions shall be the specified humidity control setting or the humidity calculated with Equation 4-4 whichever
is lower If no humidity control setting is specified the control setting shall be 50 RH
4323 Indoor Design Humidity with Dehumidification without Air-Conditioning If the building is designed
to be dehumidified with humidity-controlled dehumidification equipment and cooling equipment is not present or
not operating the indoor design humidity shall be the humidity control setting or the humidity calculated with
Equation 4-1 whichever is lower If no humidity control setting is specified the control setting shall be 50 RH
433 Indoor Design Humidity Full Parametric Calculation Full parametric evaluation of indoor humidity
requires comprehensive inputs to support the analysis of the hygrothermal response and dynamic hygrothermal
flux contribution of building elements finishes and furniture (hygric buffering) The analysis shall include thermaland mass balances and shall use simulation algorithms and time-step intervals that capture hygrothermal response
of sensitive materials and conditions
Required inputs include(a) hygrothermal properties of building materials finishes and furniture
(b) design initial moisture conditions (in accordance with Section 41)
(c) design indoor temperatures (in accordance with Section 42)
(d) design ventilation rates (in accordance with Section 43213 or 43214)
(e) design moisture generation rates (in accordance with Section 43211 or 43212)
(f) effect of active dehumidification systems
(g) design pressure data (in accordance with Section 441)
(h) design weather data (in accordance with Section 45)(i) design rain loads (in accordance with Section 46)
44 Design Air Pressure Differentials and Flows
Analysis of the effect of air pressure differentials and air flows is optional If the effect is not considered in
the design analysis this shall be expressly stated in the report If the effect is included Section 441 shall apply
441 Effect of Air Pressure Differentials Included in Design Analysis If the indoor air pressure differential
between indoors and outdoors is controlled that air pressure differential shall be used in the design analysis B-11
If the indoor air pressure differential is not managed one of two alternative procedures shall be followed
4411 Design Air Pressure Differential Alternative 1 The design air pressure differential shall be calculated
from design ventilation rates including the planned fresh air supply and exhaust rates the building air tightnesswind pressures using Moisture Design Weather Data (Section 45) and stack pressure (Section 4413)
4412 Design Air Pressure Differential Alternative 2 A design indoor air pressure differential of +5 Pa (002
in wc) above outdoor air pressure (air flow to the exterior) shall be assumed used when the 24-hour running
average outdoor temperature is below the indoor design temperatureduring the heating season and ndash 5 Pa (air flow
to the interior) when the 24-hour running average outdoor temperature is above the indoor design temperature
during the cooling season B-12
Stack pressure differential at the top of the wall of the top floor shall be calculated (Section 4413) for buildings
taller than three stories and used as the design indoor pressure differential if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 10 of 24
4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 11 of 24
U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 7 of 24
Table 431 Design indoor RH Simplified Method
Note To daily = Daily average outdoor temperature
- 20 - 10 0 10 20 30 20
30
40
50
60
70
80
I n d o o r D e s i g n R H [ ]
Daily Average Outdoor Temperature [degC]
68
Daily Average Outdoor Temperature [degF]
14
Figure 431 Design indoor relative humidity Simplified Method
432 Indoor Design Humidity Intermediate Method In this method indoor design humidity is determined
from hourly weather and depends on the season (Section 42) and the type of HVAC equipment
4321 Indoor Design Humidity without Dehumidification or Air-conditioning This section applies during
heating and temperature ldquofloatrdquo conditions as determined in Section 42 when cooling and dehumidification
equipment is not present or not operating Indoor vapor pressure for moisture design purposes shall be determined
using the following mass balance equation B-7
Q
mc p p h oi
24
(4-1)
where
pi = indoor vapor pressure Pa (inHg)
po24h = 24-hour running average outdoor vapor pressure Pa (in Hg)
c = 136 times 105 Pamiddotm3kg (107 inHgmiddotft3lb)
m = design moisture generation rate kgs (lbh) (in accordance with Sections 43211 and 2)
Q = design ventilation rate m3s (cfm) (in accordance with Sections 43213 and 4)
Daily Average
Outdoor Temperature
degC
Design RH
(Based on degC)
Daily Average
Outdoor Temperature
degF
Design RH
(Based on degF)
Below -10degC 40 Below 14degF 40
-10degCle To dailyle 20degC 40 + (To daily+10) 14degFle To dailyle 68degF 40 + (To daily-14)18Above 20degC 70 Above 68degF 70
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 8 of 24
43211 Residential Moisture Generation Design values for residential moisture generation
m are based
on the expected number of occupants For design purposes a minimum of two occupants is assumed with an
additional occupant for each bedroom in addition to the master bedroom Design moisture generation rates are
given in Table 432 B-8
Table 432 Residential design moisture generation rates Number of
Bedrooms Number of Occupants
Moisture generation rate
1 bedroom 2 8 Lday 09 x 10-4 kgs 07 lbh
2 bedrooms 3 12 Lday 14 x 10-4 kgs 11 lbh
3 bedrooms 4 14 Lday 16 x 10-4 kgs 13 lbh
4 bedrooms 5 15 Lday 17 x 10-4 kgs 14 lbh
Additional bedrooms +1 per bedroom +1 Lday +01 x 10-4 kgs +01 lbh
If the home contains a jetted tub installed in a room without an automatically controlled (eg humidistat) exhaust
fan add 13 Lday or 015 x 10-4 kgs (012 lbh)
43212 Moisture Generation for Other Occupancies For other occupancies moisture generationdesign values shall be appropriate for the intended use of the building If the appropriate moisture generation rates
are not available for the intended use the simplified method (Section 431) shall be used
43213 Designed Ventilation Design ventilation rates shall be used for the calculation of design indoor
vapor pressure (Equation 4-1) The design ventilation rate to be used is the expected continuous ventilation rate
For intermittent ventilation systems ventilation effectiveness shall be accounted for according to ANSIASHRAE
Standard 6222
43214 Non-Designed Ventilation In buildings without a designed ventilation system the following
default ventilation rates shall be used for purposes of calculating the design indoor vapor pressure (Equation 4-1)
B-9
New buildings standard construction air exchange rate of 02 ach
Q = 56 x 10-5 V m3 s (4-2a)
where V is the building volume (m3) or
Q = 00033V cfm (4-2b)
where V is the building volume (ft3)
New buildings airtight construction air exchange rate of 01 ach
Q = 28 x 10-5
V m3
s (4-3a)
where V is the building volume (m3) or
Q = 00017V cfm (4-3b)
where V is building volume (ft3)
4322 Indoor Design Humidity with Air-Conditioning If the air-conditioning equipment is running and is
controlled solely by thermostat the design indoor humidity shall be derived from the following equation
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 9 of 24
wi= 0004+04w0 (4-4)
where
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis
kgkg (lblb) B-10
If the building is air-conditioned with humidity-controlled equipment the indoor humidity design
conditions shall be the specified humidity control setting or the humidity calculated with Equation 4-4 whichever
is lower If no humidity control setting is specified the control setting shall be 50 RH
4323 Indoor Design Humidity with Dehumidification without Air-Conditioning If the building is designed
to be dehumidified with humidity-controlled dehumidification equipment and cooling equipment is not present or
not operating the indoor design humidity shall be the humidity control setting or the humidity calculated with
Equation 4-1 whichever is lower If no humidity control setting is specified the control setting shall be 50 RH
433 Indoor Design Humidity Full Parametric Calculation Full parametric evaluation of indoor humidity
requires comprehensive inputs to support the analysis of the hygrothermal response and dynamic hygrothermal
flux contribution of building elements finishes and furniture (hygric buffering) The analysis shall include thermaland mass balances and shall use simulation algorithms and time-step intervals that capture hygrothermal response
of sensitive materials and conditions
Required inputs include(a) hygrothermal properties of building materials finishes and furniture
(b) design initial moisture conditions (in accordance with Section 41)
(c) design indoor temperatures (in accordance with Section 42)
(d) design ventilation rates (in accordance with Section 43213 or 43214)
(e) design moisture generation rates (in accordance with Section 43211 or 43212)
(f) effect of active dehumidification systems
(g) design pressure data (in accordance with Section 441)
(h) design weather data (in accordance with Section 45)(i) design rain loads (in accordance with Section 46)
44 Design Air Pressure Differentials and Flows
Analysis of the effect of air pressure differentials and air flows is optional If the effect is not considered in
the design analysis this shall be expressly stated in the report If the effect is included Section 441 shall apply
441 Effect of Air Pressure Differentials Included in Design Analysis If the indoor air pressure differential
between indoors and outdoors is controlled that air pressure differential shall be used in the design analysis B-11
If the indoor air pressure differential is not managed one of two alternative procedures shall be followed
4411 Design Air Pressure Differential Alternative 1 The design air pressure differential shall be calculated
from design ventilation rates including the planned fresh air supply and exhaust rates the building air tightnesswind pressures using Moisture Design Weather Data (Section 45) and stack pressure (Section 4413)
4412 Design Air Pressure Differential Alternative 2 A design indoor air pressure differential of +5 Pa (002
in wc) above outdoor air pressure (air flow to the exterior) shall be assumed used when the 24-hour running
average outdoor temperature is below the indoor design temperatureduring the heating season and ndash 5 Pa (air flow
to the interior) when the 24-hour running average outdoor temperature is above the indoor design temperature
during the cooling season B-12
Stack pressure differential at the top of the wall of the top floor shall be calculated (Section 4413) for buildings
taller than three stories and used as the design indoor pressure differential if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 10 of 24
4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 11 of 24
U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 8 of 24
43211 Residential Moisture Generation Design values for residential moisture generation
m are based
on the expected number of occupants For design purposes a minimum of two occupants is assumed with an
additional occupant for each bedroom in addition to the master bedroom Design moisture generation rates are
given in Table 432 B-8
Table 432 Residential design moisture generation rates Number of
Bedrooms Number of Occupants
Moisture generation rate
1 bedroom 2 8 Lday 09 x 10-4 kgs 07 lbh
2 bedrooms 3 12 Lday 14 x 10-4 kgs 11 lbh
3 bedrooms 4 14 Lday 16 x 10-4 kgs 13 lbh
4 bedrooms 5 15 Lday 17 x 10-4 kgs 14 lbh
Additional bedrooms +1 per bedroom +1 Lday +01 x 10-4 kgs +01 lbh
If the home contains a jetted tub installed in a room without an automatically controlled (eg humidistat) exhaust
fan add 13 Lday or 015 x 10-4 kgs (012 lbh)
43212 Moisture Generation for Other Occupancies For other occupancies moisture generationdesign values shall be appropriate for the intended use of the building If the appropriate moisture generation rates
are not available for the intended use the simplified method (Section 431) shall be used
43213 Designed Ventilation Design ventilation rates shall be used for the calculation of design indoor
vapor pressure (Equation 4-1) The design ventilation rate to be used is the expected continuous ventilation rate
For intermittent ventilation systems ventilation effectiveness shall be accounted for according to ANSIASHRAE
Standard 6222
43214 Non-Designed Ventilation In buildings without a designed ventilation system the following
default ventilation rates shall be used for purposes of calculating the design indoor vapor pressure (Equation 4-1)
B-9
New buildings standard construction air exchange rate of 02 ach
Q = 56 x 10-5 V m3 s (4-2a)
where V is the building volume (m3) or
Q = 00033V cfm (4-2b)
where V is the building volume (ft3)
New buildings airtight construction air exchange rate of 01 ach
Q = 28 x 10-5
V m3
s (4-3a)
where V is the building volume (m3) or
Q = 00017V cfm (4-3b)
where V is building volume (ft3)
4322 Indoor Design Humidity with Air-Conditioning If the air-conditioning equipment is running and is
controlled solely by thermostat the design indoor humidity shall be derived from the following equation
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 9 of 24
wi= 0004+04w0 (4-4)
where
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis
kgkg (lblb) B-10
If the building is air-conditioned with humidity-controlled equipment the indoor humidity design
conditions shall be the specified humidity control setting or the humidity calculated with Equation 4-4 whichever
is lower If no humidity control setting is specified the control setting shall be 50 RH
4323 Indoor Design Humidity with Dehumidification without Air-Conditioning If the building is designed
to be dehumidified with humidity-controlled dehumidification equipment and cooling equipment is not present or
not operating the indoor design humidity shall be the humidity control setting or the humidity calculated with
Equation 4-1 whichever is lower If no humidity control setting is specified the control setting shall be 50 RH
433 Indoor Design Humidity Full Parametric Calculation Full parametric evaluation of indoor humidity
requires comprehensive inputs to support the analysis of the hygrothermal response and dynamic hygrothermal
flux contribution of building elements finishes and furniture (hygric buffering) The analysis shall include thermaland mass balances and shall use simulation algorithms and time-step intervals that capture hygrothermal response
of sensitive materials and conditions
Required inputs include(a) hygrothermal properties of building materials finishes and furniture
(b) design initial moisture conditions (in accordance with Section 41)
(c) design indoor temperatures (in accordance with Section 42)
(d) design ventilation rates (in accordance with Section 43213 or 43214)
(e) design moisture generation rates (in accordance with Section 43211 or 43212)
(f) effect of active dehumidification systems
(g) design pressure data (in accordance with Section 441)
(h) design weather data (in accordance with Section 45)(i) design rain loads (in accordance with Section 46)
44 Design Air Pressure Differentials and Flows
Analysis of the effect of air pressure differentials and air flows is optional If the effect is not considered in
the design analysis this shall be expressly stated in the report If the effect is included Section 441 shall apply
441 Effect of Air Pressure Differentials Included in Design Analysis If the indoor air pressure differential
between indoors and outdoors is controlled that air pressure differential shall be used in the design analysis B-11
If the indoor air pressure differential is not managed one of two alternative procedures shall be followed
4411 Design Air Pressure Differential Alternative 1 The design air pressure differential shall be calculated
from design ventilation rates including the planned fresh air supply and exhaust rates the building air tightnesswind pressures using Moisture Design Weather Data (Section 45) and stack pressure (Section 4413)
4412 Design Air Pressure Differential Alternative 2 A design indoor air pressure differential of +5 Pa (002
in wc) above outdoor air pressure (air flow to the exterior) shall be assumed used when the 24-hour running
average outdoor temperature is below the indoor design temperatureduring the heating season and ndash 5 Pa (air flow
to the interior) when the 24-hour running average outdoor temperature is above the indoor design temperature
during the cooling season B-12
Stack pressure differential at the top of the wall of the top floor shall be calculated (Section 4413) for buildings
taller than three stories and used as the design indoor pressure differential if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 10 of 24
4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 11 of 24
U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 9 of 24
wi= 0004+04w0 (4-4)
where
wi = indoor design humidity ratio kgkg (lblb)
w0 = mean coincident design outdoor humidity ratio for cooling 1 annual basis
kgkg (lblb) B-10
If the building is air-conditioned with humidity-controlled equipment the indoor humidity design
conditions shall be the specified humidity control setting or the humidity calculated with Equation 4-4 whichever
is lower If no humidity control setting is specified the control setting shall be 50 RH
4323 Indoor Design Humidity with Dehumidification without Air-Conditioning If the building is designed
to be dehumidified with humidity-controlled dehumidification equipment and cooling equipment is not present or
not operating the indoor design humidity shall be the humidity control setting or the humidity calculated with
Equation 4-1 whichever is lower If no humidity control setting is specified the control setting shall be 50 RH
433 Indoor Design Humidity Full Parametric Calculation Full parametric evaluation of indoor humidity
requires comprehensive inputs to support the analysis of the hygrothermal response and dynamic hygrothermal
flux contribution of building elements finishes and furniture (hygric buffering) The analysis shall include thermaland mass balances and shall use simulation algorithms and time-step intervals that capture hygrothermal response
of sensitive materials and conditions
Required inputs include(a) hygrothermal properties of building materials finishes and furniture
(b) design initial moisture conditions (in accordance with Section 41)
(c) design indoor temperatures (in accordance with Section 42)
(d) design ventilation rates (in accordance with Section 43213 or 43214)
(e) design moisture generation rates (in accordance with Section 43211 or 43212)
(f) effect of active dehumidification systems
(g) design pressure data (in accordance with Section 441)
(h) design weather data (in accordance with Section 45)(i) design rain loads (in accordance with Section 46)
44 Design Air Pressure Differentials and Flows
Analysis of the effect of air pressure differentials and air flows is optional If the effect is not considered in
the design analysis this shall be expressly stated in the report If the effect is included Section 441 shall apply
441 Effect of Air Pressure Differentials Included in Design Analysis If the indoor air pressure differential
between indoors and outdoors is controlled that air pressure differential shall be used in the design analysis B-11
If the indoor air pressure differential is not managed one of two alternative procedures shall be followed
4411 Design Air Pressure Differential Alternative 1 The design air pressure differential shall be calculated
from design ventilation rates including the planned fresh air supply and exhaust rates the building air tightnesswind pressures using Moisture Design Weather Data (Section 45) and stack pressure (Section 4413)
4412 Design Air Pressure Differential Alternative 2 A design indoor air pressure differential of +5 Pa (002
in wc) above outdoor air pressure (air flow to the exterior) shall be assumed used when the 24-hour running
average outdoor temperature is below the indoor design temperatureduring the heating season and ndash 5 Pa (air flow
to the interior) when the 24-hour running average outdoor temperature is above the indoor design temperature
during the cooling season B-12
Stack pressure differential at the top of the wall of the top floor shall be calculated (Section 4413) for buildings
taller than three stories and used as the design indoor pressure differential if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 10 of 24
4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 11 of 24
U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 10 of 24
4413 Stack Pressure Differential Stack pressure at the top of the wall of the top floor shall be calculated for
buildings taller than three stories and used as the design indoor pressure if greater than 5 Pa (002 in wc) unless
the building design includes effective measures to pressure-isolate each floor
The stack pressure differential at the top of the wall of the top floor shall be estimated using the following
equation B-13
Δ P s=C ((T i-T o )T i ) gH2 (4-5)
where in metric units
Δ P s = design stack pressure (Pa)
C = conversion factor (equals 1 for metric units)
= density of outdoor air (12 kgm3)
T o = outdoor temperature (K)
T i = indoor temperature (K)
g = gravitational constant (981 ms2) and
H = height of the building (m)
where in I-P units
Δ P s = design stack pressure (in of water)C = conversion factor (equals 000598 (in of water middotftmiddots2lb)
= density of outdoor air (0075 lbft3)
T o = outdoor temperature (R)
T i = indoor temperature (R)
g = gravitational constant (322 fts2) and
H = height of the building (ft)
If the airtightness of the envelope is known it shall be used to calculate the air flow rate through the
envelope at the design pressure If the airtightness is not known an airtightness of 00008 in 2ft2 (0055 cm2m2)
shall be used in an airtight building and 00042 in2ft2 (029 cm2m2) for standard construction With a design
pressure of 5 Pa this translates into an air leakage rate of 00031 cfmft2 (0016 L(smiddotm2)) in an airtight building
and 0016 cfmft2
(0084 L(smiddotm2
)) for standard constructionB-14
A description of the air flow pathways and a rationale for that selection shall be reported
45 Moisture Design Weather Data The analysis shall be performed using a minimum of 10 consecutive years of weather data or using the
Moisture Design Reference Years weather data The weather data shall include hourly data for
(a) Dry bulb air temperature
(b) Vapor pressure or dew point temperature wetbulb temperature relative humidity or humidity ratio
(c) Total solar insolation on a horizontal surface
(d) Average wind speed and direction
(e) Rainfall
(f) Cloud index
46 Design Rain Loads on Walls B-15
Design rain loads must be determined for walls exposed to rain In the absence of a comprehensive wind-
driven rain analysis the amount of rain striking a vertical surface shall be calculated using the following equation
B-16
r bv= F E F D F L U cos r h (46)
where
F E = rain exposure factor
F D = rain deposition factor
F L = empirical constant 02 kgs(m3mm) in SI 046 lbh(ft2miin) in I-P
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 11 of 24
U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 11 of 24
U = hourly average wind speed at 10 m height ms (mih)
= angle between wind direction and normal to the wall (Fig 461)
r h = rainfall intensity horizontal surface mmh (inh)
r bv = rain deposition on vertical wall kg(m2h) (lb(ft2h))
Wind
Direction
Figure 461 Plan view of building with definition of wind angle
The exposure factor FE is influenced by the topography surrounding the building and height of the
building Recommended values are given in Table 461 B-17
TABLE 461 Exposure factor
Terrain OpenSevere Medium Sheltered
Height (m)
lt10 13 10 07
10 ndash 15 13 11 08
15 - 20 14 12 0920 - 30 15 13 11
30 - 40 15 14 12
40 - 50 15 15 13
gt 50 15 15 15
Open Severe exposure includes hilltops coastal areas and funneled wind (eg from tall buildings nearby
Sheltered exposure includes shelter from trees nearby buildings or a valley
The following deposition factors shall be used
(a) Walls on pitched below a steep-slope roof building FD = 05 FD = 035(b) Walls on flat below a low-slope roof buildings FD = 10 FD = 05
(c) Walls subject to rain runoff FD = 2 FD =10B-18
461 Rain penetration In the absence of specific full scale test methods and data for the as-built exterior wall
system being considered the default value for water penetration through the exterior surface is 1 of the water reaching that exterior surfaceB-19 The deposit site for the water shall be the exterior surface of the water-resistive
barrierB-20 If a water-resistive barrier is not provided then the deposit site shall be described and a technical
rationale for its selection shall be provided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 12 of 24
5 CRITERIA FOR SELECTING ANALYTICAL PROCEDURES This section sets minimum acceptable criteria for analytical tools capable of analyzing thermal and
moisture transfer and conditions in building envelope components The analytic procedure shall be transient with a
maximum time step of one hour As a minimum requirement the procedure shall have the ability to include
(a) Energy transport including temperature effects of phase change
(b) Material properties as a function of moisture content(c) Water (liquid and vapor) transport including
Capillary transport
Moisture deposition on surfaces
Storage in materials
Vapor diffusion
Water leakage
If the design includes a ventilated cavity the analysis shall include the effects of the cavity
The analytic procedure shall provide the following output
(a) Temperature and surface relative humidity at each surface and at the interface of the material layers
(b) Average temperature for each material layer
(c) Average moisture content for each material layer
6 MOISTURE PERFORMANCE EVALUATION CRITERIA
This section sets performance criteria that shall be met to minimize the undesirable effects of moisture in a
building or building envelope B-21 These criteria apply to all materials and surfaces except the exterior surface of
the building envelope
61 Conditions Necessary to Minimize Mold Growth
In order to prevent minimize problems associated with mold growth on the surfaces of components of
building envelope assemblies all of the following conditions shall be met B-22
(a) 30-day running average surface RH lt 80 when the 30-day running average surface temperature is between
5C (41F) and 40C (104F) and(b) 7-day running average surface RH lt 98 when the 7-day running average surface temperature is between 5C
(41F) and 40C (104F) and
(c) 24-h running average surface RH lt 100 when the 24-h running average surface temperature is between 5C
(41F) and 40C (104F)
Materials that are naturally resistant to mold growth (eg concrete masonry glass and metals) or have
been chemically treated to resist mold growth (eg fungicide-treated cellulose based materials) may be able to
resist higher surface relative humidities andor to resist for longer periods as specified by the manufacturer The
criteria used in the evaluation shall be stated in the report
62 Corrosion
Requirements for prevention of corrosion shall be derived from the properties and function of the particular metals used in construction If no such information is available the 30-day running average of hourly
values of surface RH of the metal shall remain less than 80 B-23
63 Structural Degradation
Structural damage due to moisture shall be avoided For wood and wood products recurring moisturecontents above the fiber saturation point for longer than one week shall be avoidedB-24 Window condensation for a
continuous period of 24 hours or more shall be avoided
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 13 of 24
7 REPORTING
The following reporting requirements shall be met
71 Provide a description of the building envelope assembly
Assembly
Type (wall roof etc)Orientation
Surface coefficients
Air space locations and air space ventilation rates with outdoor air
Ventilation rate and locations of air spaces
List of components materials (include reference source of data)
72 Provide data on each of the components materials in the building envelope assembly
Component Material description
Thickness
Density
Thermal conductivity and its dependency on temperature and moisture content if applicable
Specific heat (heat capacity)Vapor permeance or permeability
Sorption isotherm
Liquid diffusivity or liquid conductivity
Suction isothermInitial moisture content
Other material properties required for the analytic model possibly including
Porosity
Liquid diffusivity
Capillary saturation
Maximum saturation
Airflow permeability
73 Provide general information about the building
Procedures to protect materials from wetting during construction are specified Construction sequence to
dissipate moisture provided (YN) (Section 41)
Are the operating temperatures for the building specified (YN) (Section 42)
Are HVAC equipment and controls included in the design (YN) (Section 43)
Which indoor design humidity method is selected
Simplified method (Section 431)
Intermediate method see separate section below
Full parameter method (Section 433)
Effects of air flow are considered (Section 44)
no
yes (Section 441)If effects of air flow are considered
Design air pressures managed and verified (YN)
Airtightness known (YN)
Weather data (moisture Design Reference Year or 10 years consecutive) (Section 45)
Exposure factor (07 to 15) (Section 461)
Deposition factor (05 1)
Analytic program name and description (Section 5)
Additional inputs
Thermal resistance as function of temperature
other (describe)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 14 of 24
74 For users of the intermediate method of determining indoor design humidity only (Section 4321) provide the
following
Residential or non-residential occupancy
Moisture generation rate (Sections 43211 and 43212)
Designed ventilation system
Number of design air changes per hour (Sections 43213 and 4)Building volume
Resulting ventilation rate
For thermostat-controlled air conditioning (Section 4322)
Mean coincident outdoor design humidity ratio for cooling
Resulting design indoor humidity
For humidistat-controlled air-conditioning (Section 4322) or dehumidification (Section 4323)
Humidity control setting
75 Provide the criteria used and provide results
Criteria used ( 80 Surface RHother)
Moisture content and coincident temperatures of materials
Outcome (PassFail)
8 REFERENCES
1 Standard 55-2004 Thermal Environmental Conditions for Human Occupancy American Society of HeatingRefrigerating and Air Conditioning Engineers Atlanta GA
2 Standard 622-20042007 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2224
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 1524
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 15 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX A FLOW CHARTS
Start moisture design
Define building assembly
Assign material properties
Select initial conditions (41)
Select outdoor climate (45)
Select exposure conditions (46)
Determine indoor conditions(42-44 also flow chart 2)
Perform analysis (5)
Acceptable
performance (6)
Add initial drying
procedure
Change in con-
struction design
Report
results (7)
Change
in HVAC
design
yes
yes
no
no
no
yes
Figure A-1 Flow chart of moisture-control design process using Standard 160
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 1724
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 1924
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2224
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 1624
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 16 of 24
Figure A-2 Flow chart of process for finding indoor design humidity
Section 42
Use specified
design
humidity
Use default
values
Indoor
humidity
known
yes no
Section 44
UseFlowchart 3
Simplified
method (431)
Intermediate
method (432)
Full
parameter
method (433)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 1824
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 1724
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 17 of 24
Figure A-3 Flow chart of process for finding indoor design humidity by the intermediate method
Intermediate
method (432)
Air-conditioner
on
Determine
moisture
generation
(43211 or 2)
Determine
ventilationrate
(43213 or 4)
Calculate
humidity
(Eq 41)
Section 44
Calculatehumidity
(Eq 44)
Humidistat
control or
dehumidifier
yes no
yes no
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 44 gt
set oint
Use RH
setpoint
yes no Use calculated
humidity (Eq
44)
yes no
De-
humidifier
RH control
setpoint
specified
Setpoint =
50 RH
RH from
Eq 41 gt
set oint
Use calculated
humidity (Eq
41)
Use RH
setpoint
yesno
noyes
yes no
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 1824
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2024
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 18 of 24
INFORMATIVE ANNEX B Humidity ratios (middot10-3) as a function of dry-bulb temperature and coincident
wet-bulb temperatures at standard atmospheric pressure (101300 Pa 1469 psi)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)189 194 0 06 11 17 22 28 233 39 44 5 56 61 67
200 132 138 146 68
211 127 133 141 150 157 70
222 122 129 137 145 152 160 168 72
233 118 124 132 140 147 156 163 172 180 74
244 113 119 127 136 142 151 158 167 175 184 192 76
256 108 114 122 130 137 146 153 162 170 179 187 197 07 78
267 103 110 118 126 133 141 148 157 165 174 182 192 02 11 21 80
278 8 105 113 121 128 136 144 153 160 170 177 187 197 06 16 82
289 4 100 108 116 123 132 139 148 155 165 173 182 192 01 11 84
300 9 96 104 112 118 127 134 143 151 160 168 178 188 196 07 86
311 4 91 9 107 114 122 130 138 146 155 163 173 183 192 02 88
322 0 86 4 102 109 118 125 134 141 150 158 168 178 187 197 90
333 5 82 0 8 104 113 120 129 136 146 154 163 173 182 192 92
344 1 77 5 3 100 108 116 124 132 141 149 159 169 177 188 94
356 6 72 0 8 4 103 110 119 127 136 144 154 164 172 182 96
367 1 67 5 3 0 9 106 114 122 131 139 149 159 167 178 98
378 6 63 1 9 6 4 101 110 117 127 134 144 154 162 173 100
389 2 58 6 4 1 9 6 105 113 122 130 139 149 158 168 102
400 7 54 2 0 6 5 2 100 108 117 125 135 144 153 163 104
411 49 7 5 2 0 7 6 103 112 120 130 140 148 159 106
422 2 0 7 5 2 1 99 108 116 125 135 144 154 108
433 6 2 1 8 7 94 103 111 121 130 139 149 110
66 67 68 69 70 71 72 73 74 75 76 78 79 80 81
Coincident Wet-bulb Temperature (degF)
Dry-
bulb
(degC)
Coincident Wet-bulb Temperature (degC) Dry-
bulb
(degF)106 111 117 122 128 133 139 144 15 156 161 167 172 178 183
200 0 45 50 56 2 7 73 78 85 2 7 104 110 118 124 68
211 5 40 46 51 7 2 68 74 80 7 3 100 106 113 119 70222 1 36 41 46 2 8 64 69 76 2 8 95 101 108 115 72
233 6 31 37 42 8 3 59 64 71 8 3 90 96 104 110 74
244 2 26 32 37 3 8 55 60 66 3 9 86 92 99 105 76
256 22 27 32 8 3 50 55 61 8 4 81 87 94 100 78
267 23 28 4 9 45 50 57 4 9 76 82 89 6 80
278 23 9 4 40 46 52 9 5 72 77 85 1 82
289 5 0 36 41 48 4 0 67 73 80 6 84
300 5 31 37 43 0 5 62 68 75 2 86
311 27 32 38 5 1 58 64 71 7 88
322 34 1 6 53 59 66 2 90
333 6 2 49 54 62 8 92
344 7 44 50 57 3 94
356 39 45 52 8 96
367 40 48 4 98378 9 100
389 4 102
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Coincident Wet-bulb Temperature (degF)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2024
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2124
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2224
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2324
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 1924
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 19 of 24
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX B COMMENTARY ON STANDARD 160
B-1Although this standard applies to all parts of all buildings additional information may be needed for the proper
design of foundations and ventilated cavities such as crawl spaces and attics This standard assumes that
appropriate measures have been taken to limit bulk water entry into the building and building envelope For
information and guidance on selection and installation of materials and systems to avoid water damage the
following documents may be of help
Window installation ASTM Standard E2112 Standard Practice for Installation of Exterior Windows Doors
and Skylights
Water penetration ASTM Standard E2266-04 Standard Guide for Design and Construction of Low-Rise
Frame Building Wall Systems to Resist Water Intrusion Water Management Guide Joseph W Lstiburek
Building Science Press 2006
ASTM Standard E241-04 Standard Guide for Limiting Water-Induced Damage to Buildings
Ice dam prevention Attic Venting Attic Moisture and Ice Dams Canadian Mortgage and Housing
Corporation About Your House series C 13 Rose WB TenWolde A 2002 Venting of attics and cathedral
ceilings ASHRAE Journal vol 44 no 10 (October) pp 26-33
Roof water and groundwater management Building Foundation Design Handbook K Labs J Carmody and
R Sterling Underground Space Center University of Minnesota 1988 Available from National Technical
Information Service (NTIS) ASHRAE 2005 Handbook Fundamentals 2410-2411 Investigating diagnosing
and treating your damp basement 1992 Canada Mortgage and Housing Corporation Water Management
Guide Joseph W Lstiburek Building Science Press 2006
Flooding ASCESEI 24-05 Flood Resistant Design and Construction American Society of Civil Engineers
Structural Engineering Institute Reston VA 2006
Construction moisture Southern Pine Council ndash Proper Lumber Storage httpwwwsouthernpinecomlumberstorageshtml Gypsum Association Document ldquoGA 238 Guidelines for
Prevention of Mold Growth on Gypsum board
B-2Guidance on airtight construction can be found in ASTM E 1677 (see Annex C Bibliography) The design and
installation of a continuous airflow retarder systemair barrier should be durable be capable of withstanding design
wind loads and be continuous over the entire building envelope including continuity at
construction control and expansion joints
junctions between different building assemblies
penetrations and projections through the building assembly (eg pipes through a wall precast cladding
anchors brick ties)
the base of interior space projecting through the building assembly (eg projecting bay windows or larger cantilevered space) and
wallfloor and interiorexterior wall intersections
Refer to the source of this information Di Lenardo et al (1995) for more detail (see Annex C Bibliography)
B-3The source for the definition for Moisture Design Reference Years is International Energy Agency Annex 24
1996 (see Annex C Bibliography)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2124
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2224
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2324
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 20 of 24
B-4The choice of EMC80 for initial moisture conditions is based on the criteria for mold growth from IEA (1991)
(see Annex C Bibliography) which states (pp 6-7) ldquoTake for new designs as threshold steady-state water activity
or RH()100 for mold germination bdquoaw‟ = 08 use this value on a monthly mean basisrdquo
B-5During the heating season the indoor design temperature is assumed to be 211degC (70degF) and for the cooling
season 239degC (75degF) if air-conditioning equipment is included in the design Heating or cooling is assumed to
take place based on a 24-hour running average of hourly outdoor temperature Heating is assumed when therunning average falls below 183degC (65degF) and cooling when the running average rises above 211degC (70degF) if
air-conditioning equipment is included in the design When the 24-h running average outdoor temperature falls
between 183degC (65degF) and 211degC (70degF) the indoor temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the
24-h running average outdoor temperature If no air-conditioning equipment is included in the design the indoor
temperature is assumed to ldquofloatrdquo at 28degC (5degF) above the 24-h running average outdoor temperature when the 24-
h running average temperature is above 183degC (65degF)
B-6The simplified method for indoor design humidity is based on data from buildings without air-conditioning
While the standard allows use of this method for air-conditioned buildings it should be understood that humidity
conditions in air-conditioned buildings tend to be lower The intermediate method provides more realistic
conditions for air-conditioned buildings except when the building is cooled by radiant heat or swamp coolers The
simplified method may also produce high values for buildings without air-conditioning in dry climates even withair-conditioning Again the intermediate of or full-parameter analysis would be preferable
B-7Indoor humidity conditions are the result of a water vapor mass balance between water vapor production and
water vapor removal For reasons of simplification Equation 41 accounts for the effect of water vapor stored inhygroscopic materials by using a 24-hour running average Water vapor transfer by vapor diffusion through the
exterior envelope is ignored It also ignores the effect of initial moisture conditions (ie ldquoconstruction moisturerdquo)
on indoor humidity We recommend that Equation 41 also be used when the building is exclusively cooled by
radiant cooling
B-8The numbers in Table 432 are based on published values for residential moisture production rates The
rationale is described by TenWolde and Walker (2001) (see Annex C Bibliography) The values represent the
approximate 70 percentile (ie 70 of homes should have moisture generation rates less than the rates in Table41) Moisture production for jetted tubs is based on Angell and Olson (1988) (see Annex C Bibliography)
B-9The default design ventilation rate for buildings (standard construction) without aThe non-designed ventilation
rate system for standard construction is based on data by Sherman and Dickerhoff (1998) (see Annex C
Bibliography) and represents the 70 percentile of normalized air leakage for new construction (1995) ie 70 of
new homes have an average ventilation rate greater than 02 air changes per hour The default ventilation rate for
airtight construction is set at half that level
B-10The mean coincident design outdoor humidity conditions needed for Equation 44 are reported in the 2005
ASHRAE Handbook of Fundamentals (CD ROM version only see Annex C Bibliography) chapter 28 table 1
columns 9c and 9d They are reported in terms of drybulb and mean coincident wetbulb temperatures Conversion
to humidity ratio can be accomplished using readily available psychrometric tables charts or tools available on theinternet Values for the corresponding design humidity ratio w0 at standard atmospheric pressure can be found in
Annex B or an approximation can be obtained with the following equation
w0 (dbwb) = wwetbulb at saturation ndash 024 (Tdrybulb-Twetbulb)
where wwetbulb at saturation is the humidity ratio of saturated air at the wetbulb temperature (temperatures in degF)
In SI units the formula is
w0 (dbwb) = wwetbulb at saturation ndash 043 (Tdrybulb-Twetbulb)
with temperatures in degC
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2124
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2224
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2324
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2124
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 21 of 24
To obtain an approximate adjustment for different altitudes and ambient air pressures multiply the result from
Annex B or the equations above with the ratio of the standard atmospheric pressure (101300 Pa 1569 psi) to the
actual atmospheric pressure
B-11It is recommended that controlled air pressure differences included in the building design be verified by
measurement at the time of building commissioning
B-12This standard does not account for large mechanically-induced air pressures
B-13Equation 45 for buildings over three stories high assumes that the reference pressure (neutral pressure plane) is
at half the building height The pressure difference at the top of the wall of the top floor shall be calculated because
a) it is greater at that location and b) it is in the most detrimental direction (ie from inside to outside in winter
and outside to inside in summer) This assumes that wall design does not vary with building height
B-14 Air Default air leakage rates are based on the minimum leakage rates for an air barrier and rigid sheathing at 5
Pa 2001 ASHRAE Handbook--Fundamentals (see Annex C Bibliography) p 2615 and an assumption of a flow
exponent of 10 and a discharge coefficient of 1
B-15
This standard deals with rain penetration in walls only Roof systems are to be designed and built such thatthere is no rainwater penetration For guidance on good roof design see the NRCA Roofing and Waterproofing
Manual (2001) (see Annex C Bibliography)
B-16The formula for driving rain is a linearization of the formula developed by Lacy (1965) r v=0222Vr h088 (see
Annex C Bibliography) Lacy‟s formula assumes an average droplet size and will tend to overestimate driving
rain because it underestimates the contribution of larger drops ASTM Standard C1601-05 Standard Test Method
for Field Determination of Water Penetration of Masonry Wall Surfaces (see Annex C Bibliography) provides a
table for rain angle as a function of wind speed and of rain intensity where rainfall intensity substitutes for
raindrop size However for our purposes the simple approach of equation 46 is accurate enough especially in
light of the uncertainties in exposure factors and deposition factors
B-17
The exposure factor includes the effects of terrain (roughness and height) topography and obstructions Raindeposition on the wall has been simplified from Figures A and B The maximum values for flat roofed (10) and
pitched roofed (05) buildings are used in the standard The figures show side views of buildings with two different
types of roofIn order to determine an exposure it may be useful to refer to the American Society of Civil
Engineers who maintains a standard entitled ldquoASCESEI-07 Minimum Design Loads for Buildings and Other
Structuresrdquo (ASCE 2005) which contains wind load provisions Within the document are what is referred to as
wind exposure categories that that are used in determining the exposure of the subject building in order to
determine the magnitude of wind load on a building These predetermined exposure categories may be useful in
determining the rain deposition on the design building ASCE-07 exposure categories are
ldquoExposure category B [consists of] urban and suburban areas wooded areas or other terrain with
numerous closely spaced obstructions having the size of single-family dwellings or largerrdquo
ldquoExposure category C [consists of] open terrain with scattered obstructions having heights generally less
than 30 feet (92 meters) This category includes flat open country grasslands and all water surfaces inhurricane prone regionsrdquo
ldquoExposure category D [consists of] flat unobstructed areas and water surfaces outside hurricane prone
regions This category includes smooth mud flats slat flats and unbroken icerdquo
A fourth category was recognized up until 2005 this was ldquoExposure categor y A It consisted of heavily built-up
city centers with tall buildings However [it was determined] that in areas in close proximity to all buildings the
variability of the wind [was] too great because of local channeling and wake buffeting effectrdquo [1] As a result the
user may need to take into consideration local wind activities from regional data collection sources for use on
buildings in these types of areas
Rain deposition on the wall
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2224
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2324
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2224
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 22 of 24
10 05 10
04
035 035
05
[Note to Reviewers These two
figures are deleted in this public
review draft]
Figure A Typical values for the deposition factor FD for walls of rectangular buildings (based on British Standard BS
81041992)
Figure B Recommended values for the deposition factor FD for walls of buildings with sloped roof (based on British
Standard BS 81041992 which is listed in Appendix D Bibliography)
B-18Rain runoff onto walls may occur from roofs or impermeable non-water-absorbing wall surfaces above such as
windows The deposition factors contain a large amount of uncertainty Calculating rain deposition on buildings is
still an evolving science
B-19Full-scale mock-up tests of rain penetration into exterior walls should include the effect of windows doors andother design details Guidance of this type of testing can be found in ASTM Standards D5957-98 Standard Guide
for Flood Testing Horizontal Waterproofing Installations and E2099-00 Standard Practice for the Specification
and Evaluation of Pre-Construction Laboratory Mockups of Exterior Wall Systems (see Annex C Bibliography)
B-20For reasons of simplicity rain penetrating the exterior wall surface is assumed to be distributed uniformly on
the water water-resistive barrier
B-21Usually the criteria for mold and corrosion are the most restrictive An extensive discussion of failure criteria
can be found in Viitanen and Salonvaara (2001) (see Annex C Bibliography)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2324
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2324
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Page 23 of 24
B-22The source for the criteria for mold growth is IEA (1991) Annex XIV (see Annex C Bibliography) with added
temperature criteria
B-23Corrosion - Harriman et al (2001) (see Annex C Bibliography) describe a ldquocritical relative humidityrdquo at which
the corrosion rate becomes rapid Clean iron does not corrode until the air is practically saturated but if the air
contains a trace of sulfur dioxide (001) the critical relative humidity is 70 The critical relative humidity for copper is 87 but reduces to 80 rh with a trace of sulfur dioxide Nickel has a critical relative humidity of 70
B-24Fiber saturation of solid wood is usually taken to be around 30 MC oven dry weight basis Fiber saturation of
composite wood products such as oriented strandboard is often lower in the range of 20 to 25
(This annex is not part of this standard It is merely informative and does not contain requirements necessary for
conformance to the standard It has not been processed according to the ANSI requirements for a standard and may
contain material that has not been subject to public review or a consensus process Unresolved objectors on
informative material are not offered the right to appeal at ASHRAE or ANSI)
INFORMATIVE ANNEX C BIBLIOGRAPHY
2005 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2005
2001 ASHRAE Handbook--Fundamentals American Society of Heating Refrigerating and Air Conditioning
Engineers Atlanta GA 2001
Angell WJ and Olson WW 1988 Moisture sources associated with potential damage in cold-climate housing
In Condensation and Related Moisture Problems in Homes American Association of Housing Educators and
Building Research Council University of Illinois at Urbana-Champaign IL
ASCE ldquoMinimum Design Loads for Buildings and Other Structures American Society of Civil Engineers amp
Structural Engineers Institute Reston VA 2005
ASHRAE Terminology of Heating Ventilation Air Conditioning and Refrigeration
American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA 1992
ASTM E1677 Standard Specification for an Air Retarder Material or System for Low-rise Framed Building Walls
ASTM Conshohocken PA
British Standard BS 81041992 Code of practice for assessing exposure of walls to wind-driven rain British
Standard Institution
Standard CENTC 89 N XXX E Thermal performance of buildings ndash climatic data ndash part 3 Calculation of a
driving rain index for vertical surfaces from hourly wind and rain data
Harriman L G Bundrette R Kittler 2001 Humidity Control Design Guide for Commercia land Industrial
Buildings American Society of Heating Refrigerating and Air Conditioning Engineers Atlanta GA
International Energy Agency (IEA) 1991 Guidelines amp Practice Report Annex XIV Volume 2 Leuven
Belgium
International Energy Agency Annex 24 1996 Heat Air and Moisture Transfer in Insulated Envelope Parts
Laboratrium Bouwfysica K-U Leuven BelgiumVolume 2 Environmental Conditions (C Sanders)
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
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BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80
7272019 Std 160 PPR2 Draft (Chair Approved Rev1)
httpslidepdfcomreaderfullstd-160-ppr2-draft-chair-approved-rev1 2424
BSRASHRAE Standard 160P Criteria for Moisture-Control Design Analysis in Buildings
Second Public Review Draft (Draft Shows Independent Substantive Changes to Previous Public Review Draft)
Di Lenardo B Brown WC Dalgleish WA Kumaran K Poirier GF 1995 Technical guide for air barrier
systems for exterior walls of low-rise buildings National Research Council Canada Ottawa Ontario Canada
Kuumlnzel HM Holm A Kaufmann A 2003 Raumluftbedingungen fuumlr die Feuchteschutzbeurteilung von
Wohngebaumluden IBP Mitteilungen vol 30 427 Fraunhofer Institute for Building Physics Holzkirchen Germany
Lacy RE 1965 Driving-rain mapsand the onslaught of rain on buildings Proceedings of the RILEMCIBSymposium on Moisture Problems in Buildings Helsinki Finland
NRCA Roofing and Waterproofing Manual 5th Edition National Roofing Contractors Association Rosemount
IL 2001
Sherman MHand Dickerhoff DJ 1998 Airtightness of US Dwellings ASHRAE Transactions 104(2)
Straube JF 1998 Moisture control and enclosure wall systems PhD Thesis Civil Engineering Dept University
of Waterloo Waterloo Ontario
TenWolde A Walker I 2001 Interior moisture design loads for residences In Performance of the Exterior
Envelopes of Whole Buildings VIII American Society of Heating Refrigerating and Air Conditioning EngineersAtlanta GA
Viitanen H Salonvaara M 2001 Failure Criteria In Moisture Analysis and Condensation Control (H Trechsel
ed) chapter 4 ASTM Manual MNL 40 ASTM West Conshohocken PA p 66-80