fact or fiction - cool roofs cause condensation? · fact or fiction - cool roofs cause...
TRANSCRIPT
Fact or Fiction - Cool Roofs
Cause Condensation?
Phil Dregger, PE, RRC, FRCI
Pacific Building Consultants
Technical Roof Services, Concord, CA
July 17, 2012
International Roof Coatings Conference, Baltimore, Maryland
2
Phil Dregger, PE, RRC
© 2002 - 2012
3
Phil Dregger, PE, RRC
© 2002 - 2012
4
Phil Dregger, PE, RRC
© 2002 - 2012
5
Phil Dregger, PE, RRC
© 2002 - 2012
Phil Dregger, PE, RRC
© 2002 - 2012 6
Phil Dregger, PE, RRC
© 2002 - 2012 7
Walking the Tight Rope…
“West Coast” Roof Deck Construction
Roof Membrane
OSB/Plywood Sheathing
F/G Batt Insulation w Facer (~retarder)
Not Vented to Exterior.
Typical Winter “Wetting”, Summer “Drying”
Often Delicate Balance Avoids Problems (e.g., inside RH, reflectance, air exchange (HVAC), air intrusion).
8
Phil Dregger, PE, RRC
© 2002 - 2012
“Cool” Reroof – Balance Breaker?
Old non-cool BUR got hot, helped drying.
New “cool” roof stays much cooler, slows
drying (including drying of “leaks”).
Anecdotal Evidence – Often this makes
the difference between wood decks that
barely drying out and those that develop
fungal growth and/or deteriorate.
9
Phil Dregger, PE, RRC
© 2002 - 2012
Condensation Control
Roofs and walls need to be designed/constructed to
avoid excessive accumulation of condensation.
Cold side vapor retarders (e.g., roof coverings)
coupled with air intrusion from below can result in
severe condensation – even in moderate climates.
It only gets worse if you add a “cool” roof,
a M.A. S/Ply, or some small roof leaks.
Today focus on potential impacts of installing
“cool roofs” on low-slope commercial roofs over
wood decks with insulation below.
10
Phil Dregger, PE, RRC
© 2002 - 2012
Water Vapor Condenses
On Cold Surfaces.
Air can hold only so much
water vapor.
Warm air can hold more water
vapor than cold air.
Two Glasses – one with ice
and one without. Water vapor
condenses only on the sides of
the glass with the ice, because
the air next to the that glass is
cooler (below its dew point).
11
Phil Dregger, PE, RRC
© 2002 - 2012 12
13
Condensation Analysis - Winter (ASTM C755 procedures)
(60°F, 54%)
(70°F, 38%)
Lack of “continuity”.
13
Max Vapor Pressure
(100% RH)
14
Phil Dregger, PE, RRC
© 2002 - 2012
15
Strategy 1 – Install Vapor Retarder (or dehumidify)
15
0.1 perm
V-Retarder
16
Strategy 2 – Ventilate Below Deck (with outside air)
16
17
Strategy 3 – Add Insulation Above
17
~R19
Would adding a vapor retarder and/or
below deck venting have helped?
Probably. Were they required? Maybe, maybe not.
One thing IS clear…the roof system “designer” is
responsible to comply with applicable codes...
Ventilation of “enclosed” rafter spaces.
Vapor retarders in certain constructions.
Seals against air leakage in building envelope.
Projects w/o Architect, Specifier, or Consultant…
Who is the designer - Owner? Contractor? Manufacturer?
18
Phil Dregger, PE, RRC
© 2002 - 2012
2009 Int’l Code Council (ICC) Codes
Attics and Enclosed Rafter Spaces.
2009 Int’l Building Code (~2010 CBC)
Chapter 12, Interior Environment
1203.2 Attic Spaces - Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof framing members shall have cross ventilation for each separate space… [1503.5 refers to…]
What exactly is “an enclosed rafter space”
Does reroofing require retrofitting to comply?
Ounce of Prevention Tip
When in doubt… obtain interpretation of AHJ.
19
2009 Int’l Code Council (ICC) Codes Vapor Retarders – Definitions
2009 Int’l Building Code (IBC)
202 Definitions - Vapor Retarder Classes
Class I: 0.1 perm or less (e.g., polyethylene sheet).
Class II: 0.1 < perm ≤ 1.0 perm (e.g., kraft facer).
Class III: 1.0 < perm ≤ 10 perm (e.g., latex paint).
20
Phil Dregger, PE, RRC
© 2002 - 2012
2009 Int’l Building Code
Chapter 15, Roof Assemblies…
Definitions – A roof assembly includes a
“vapor retarder”.
Rest of Chapter - Silent regarding vapor
retarder requirements.
Tip – Check for local amendments.
2009 Int’l Code Council (ICC) Codes Vapor Retarders – Roofs
21
2009 Int’l Energy Conservation Code
Silent regarding vapor retarder requirements in roofs except:
Table 502.2(2), metal roofs with glass fiber batts
between purlins, “continuous vapor retarder… below
purlins...”
Includes consistent requirements to seal
building envelope against air infiltration
(~air retarders or vapor retarders).
2009 ICC Codes (~2010 CA Energy Code)
Vapor Retarders – Roofs
22
Phil Dregger, PE, RRC
© 2002 - 2012
2009 Int’l Energy Conservation Code
Chapter 5, Commercial
502.4 Air Leakage – The building thermal envelope
shall be durably sealed to limit infiltration… The
following shall be caulked, gasketed… or otherwise
sealed…
(1) All joints, seams, and penetrations.
(10) Attic access openings.
(11) Rim joints.
2009 ICC Codes (~2010 CA Energy Code)
Vapor Retarders / Air Leakage
23
Phil Dregger, PE, RRC
© 2002 - 2012
Air Leakage/Infiltration
Importance of Energy Code requirements to seal
“joints, seams, and penetrations” in building
envelopes under-appreciated, if even “known”.
Vapor Retarders - Definitions provided.
Limited where/when required in walls.
Very limited where/when required in roofs.
Guidelines [and reminders] Needed.
Summary - 2009 ICC Vapor Retarders / Air Leakage
24
Phil Dregger, PE, RRC
© 2002 - 2012
Vapor Retarder Guidelines
NRCA (one of oldest, useful, not discussed here)
Cold Regions Research and Engineering Laboratory (CRREL)
Oak Ridge National Laboratory (ORNL)
ANSI/ASHRAE Standards (e.g., resultant RH)
Guidelines Useful but NOT Requirements (pertinent to SOC question but not requirements
unless referenced in code or required by contract)
25
Phil Dregger, PE, RRC
© 2002 - 2012
CRREL – Retarder Guidelines:
Depending on inside relative humidity and location.
26
ORNL Guideline - WUFI Program
Avoid High Rh and H20 Accumulation
Hygrothermal model.
Considers changes in material properties with changing temp/Rh.
Provides temperature and Rh data throughout assembly and at monitor locations.
Allows comparative trials...
Download Research and Education Version:
www.ornl.gov/sci/btc/apps/moisture/ibpe_sof161.htm
27
Phil Dregger, PE, RRC
© 2002 - 2012
Guidelines Useful But Be Careful
Above Guidelines have proven reasonable over
time and are reliable in terms of judging basic
“need” (or not) for vapor retarders.
Be Careful - WUFI and other less sophisticated
roof design guidelines assume no air intrusion.
Decisions based on them may be less than
conservative if (or where) assumptions not true.
28
Phil Dregger, PE, RRC
© 2002 - 2012
Walking the Tight Rope…
West Coast Roof Deck Construction
Roof Membrane
OSB/Plywood Sheathing
F/G Batt Insulation w Facer (~retarder)
Not Vented to Exterior.
Typical Winter “Wetting”, Summer “Drying”
Sometimes Delicate Balance Avoids Problems (e.g., inside RH, reflectance, air exchange (HVAC), air intrusion).
29
Phil Dregger, PE, RRC
© 2002 - 2012
One Year Old, Unoccupied Warehouse/Office Springtime Dripping Water (+after insulation retrofit)
30
Phil Dregger, PE, RRC
© 2002 - 2012
One Year Old, Unoccupied Warehouse/Office Springtime Dripping Water (also after retrofit)
31 31
32
One Year Old, Unoccupied Warehouse/Office Springtime Dripping Water (also after retrofit)
32
Start sheathing at 28%
Start sheathing at 0% (overlay)
33
Water Not From Original Sheathing
33
Phil Dregger, PE, RRC
© 2002 - 2012
34 34
Construction Along Truss Purlins
foil facer
f/b batt
BUR, nailed base
plywood/OSB
steel truss
wood block
35 35
Best Explanation: Localized Winter Wetting
colder, less humid, some wind
warmer, more humid, no wind, “positive” pressure
36 36
Phil Dregger, PE, RRC
© 2002 - 2012
37 37
Saturated, ≥130°F at deck
Cooler, less humid inside
Best Explanation: Localized Spring Dripping (early warm weather)
38 38
Phil Dregger, PE, RRC
© 2002 - 2012
Vapor Condenses On And
Drips-Off Metal Surfaces
39 39
Phil Dregger, PE, RRC
© 2002 - 2012
“Air movement carrying the water vapor with it
is far more powerful in transporting water vapor”
[than diffusion]. (Chapter 21, page 4)
“The relative amounts of water deposited in a wall
or roof by vapor diffusion or by a current of air
cannot be calculated with certainty. Under one set
of conditions, six or seven times as much water can
be deposited as a result of air leakage as by vapor
diffusion… Under different circumstances, the rates
could be 100:1 or higher.” (Chapter 21, page 5)
Cautions about air intrusion are not new.
1989 ASHRAE Fundamentals…
40 40
Barrel Roof – Openings (for air intrusion)
41
Walking the Tight Rope…
West Coast Roof Deck Construction
Roof Membrane
OSB/Plywood Sheathing
F/G Batt Insulation w Facer (~retarder)
Not Vented to Exterior.
Typical Winter “Wetting”, Summer “Drying”
Sometimes Delicate Balance Avoids Problems (e.g., inside RH, reflectance, air exchange (HVAC), air intrusion).
42
Phil Dregger, PE, RRC
© 2002 - 2012
Phil Dregger, PE, RRC
© 2002 - 2012 43
44
45
46
“Cool” Reroof – Balance Breaker?
Old non-cool BUR got hot, helped drying.
New “cool” roof stays much cooler, slows
drying (including drying of “leaks”).
Anecdotal Evidence – Sometimes makes the
difference between wood decks barely
drying out and those that deteriorate /
develop fungal growth.
The physics agrees…
47
WUFI – BUR vs. “Cool” BUR
48
Phil Dregger, PE, RRC
© 2002 - 2012
WUFI – BUR vs. “Cool” BUR
Bottom of Plywood - Rh Mold Growth ≥80% Rh, >41°F
BUR Cool-BUR
49
Phil Dregger, PE, RRC
© 2002 - 2012
ANSI/ASHRAE Standard 160 (2009) - Criteria
for Moisture-Control Design Analysis in Buildings
Section 6 “Moisture Performance Evaluation Criteria” (as revised by Addendum A, issued late 2011).
…keep 30-day average RH < 80%
when temperatures 41°F - 104°F
50 50
Phil Dregger, PE, RRC
© 2002 - 2012
This Speaker’s Suggestions
Ask about reports of Spring roof leaks or dripping.
Comply with codes – confirm local amendments and/or code
interpretations (e.g., venting of enclosed rafter spaces).
Advise owner of condensation sometimes associated with
cool roofs, recommend adding insulation above roof deck.
Seal openings that allow air intrusion into insulated spaces, install separate air retarders where needed.
Install vapor retarders only where required/needed.
Obtain assistance with mechanical systems – an important component.
51
Phil Dregger, PE, RRC
© 2002 - 2012
Questions?
The End - Thank You.
52