the problem with and solutions for ventilated attics
TRANSCRIPT
The Problems With and Solutions for
Ventilated AtticsRCI 30TH INTERNATIONAL CONVENTION - SAN ANTONIO, TX MARCH 9, 2015
GRAHAM FINCH, MASC, P.ENG – RDH BUILDING ENGINEERING LTD.
Presentation Overview
Current Issues with Ventilated Attics
Case Study of Repairs
Attic Roof Hut Research & Monitoring Study –
Key Findings
Performance of Potential Solutions
Ongoing Research & Field Trials
An Obvious Problem
A Not So Obvious Problem
Influencers of Moisture Problems in Attics
What influences attic moisture issues &
what can we control by design?
Roof orientation (solar radiation)
Roof slope (solar radiation)
Roofing material/color
Adjacent buildings – shading
Trees – shading & debris
Outdoor climate
Indoor climate
Roof Leaks
Insulation R-value
Air leakage from house
Duct leakage in attic
Duct discharge location
Vent area and distribution
Sheathing durability
Roof maintenance
Other things
Where are we Seeing the Biggest Issues?
• Air leakage (ceiling details)
• Exhaust duct leaks & discharge location (roof, soffit, or wall)
• Inadequate venting provisions (amount, vent location, or materials)
• Outdoor moisture: night sky condensation on underside of sheathing
• Wetting through shingles/roofing (tipping the moisture balance)
Influence of Solar Radiation & Night Sky Radiation
Industry Trends – Less Heat Flow into Ventilated Attic Spaces
<1970’s attic construction with
excessive air leakage and heat loss
into the attic
1980’s to 1990’s attic construction with
moderate air leakage and heat loss into
the attic
2000’s attic construction with minimal air
leakage and heat loss into the attic
Standard Faith-Based Ventilation Approach
Air-sealing details, duct exhaust details often not provided & left up to the contractor
Alternates to Ventilated Attics
Unvented Hot Roof
(Sprayfoam applied to
underside)
Exterior Insulated &
hybrid approaches
Typical Ventilated Attic Moisture & Mold Issues
Typical Issues – Impact of Orientation
North = Soaked
South (Partially Shaded) = Damp
The Localized Nature of Air Leakage Condensation
The Localized Nature of Leaking Penetrations
The Localized Nature of Outdoor Moisture Wetting &
Night Sky Condensation
It Happens in Ventilated Low Slope & Cathedral
Ceilings Too
Other Not So Great Ideas…
So When Does it Become a Problem?
So When Does it Become a Problem?
So When Does it Become a Problem?
Case Study: Two Steps Forward, One Step Backwards
• 2007 investigation of 5 yr old large
townhouse complex
• Was experiencing all of the problems we
were and still are currently seeing
An Assortment of Typical Issues – Exhaust Ducts
An Assortment of Typical Issues – Exhaust Duct Details
An Assortment of Issues – Inadequate Ridge ‘Vent’ Material
Almost no effective net
free area, 5 layers of
filter fabric
An Assortment of Issues – Ceiling Air Leakage
Attic Remediation – 2 years Later
Full Review of Initial Contributing Factors, Air-sealing
Retrofit Ceiling Air Sealing - Sprayfoam
Ceiling Air Sealing – Poly Bags of Fun
Mold Remediation - Dry Ice Blasting
New Exhaust Vent Hoods & Attic Ridge Vents
2 Years Later Again…
The Localized Nature of Wetting
Water Leaks Around Plugged Dryer Exhaust Ducts
Lack of Dryer Exhaust Duct Maintenance
Soffit Exhaust Vent Hood Configuration Issues
Air-Sealing Issues
Air-Sealing Issues
Questioning the Effectiveness of Dry Ice Blasting against Mold?
Water Seepage through Aged & Saturated Asphalt Shingles?
Key Findings from Field Investigations & Field
Monitoring
Seeing widespread issues with
mold growth in newer wood-frame
attics in Pacific Northwest
Wetting is exceeding drying
capacity provided by ventilation
Problem is most often NOT due to
a lack of ventilation
Usual culprits of air-leakage
condensation (leaky ceiling, leaky
ducts & discharge point)
Also seeing supplemental exterior
moisture sources (night sky
condensation, rainwater seepage)
Field Monitoring Study
Research Study Premise
Controlled field monitoring study to
isolate exterior wetting
mechanisms from interior sources
(air, vapour)
To specifically evaluate impact of
orientation, slope (3:12, 4:12 and
6:12) & shingle underlay
Remove influence of air leakage or
heat gain from house
Monitor the performance of
surface treatments
Typical ventilated attic
construction with air
leakage and heat loss into
the attic
Theoretical attic with no air
leakage or heat loss into the
attic and unrestricted
ventilation – Study setup
here
Concurrent Companion Research in Pacific Northwest
Homeowner Protection Office of BC
RDH – monitoring field conditions & controlled field
study (covered here)
MH – monitoring of attic moisture levels and air-
leakage from indoors into attic spaces
FP Innovations – monitoring of effectiveness of various
surface treatments
BCIT – modeling of attic ventilation rates & moisture
movement
Roof Test Hut Field Monitoring Setup
a) 3:12 Slope roof with roofing felt underlay b) 4:12 Slope roof with roofing felt underlay
c) 6:12 Slope roof with roofing felt underlay d) 3:12 Control roof with SAM underlay
Roof Test Hut Field Monitoring Setup
Monitoring Equipment & Sensors
Moisture Content, Temperature,
Relative Humidity and surface
Condensation sensors – north and
south slopes x 4 huts
Site Boundary Conditions
0
5
10
15
20
25
300
9-2
01
2
10
-20
12
11
-20
12
12
-20
12
01
-20
13
02
-20
13
03
-20
13
04
-20
13
05
-20
13
06
-20
13
07
-20
13
08
-20
13
09
-20
13
10
-20
13
11
-20
13
12
-20
13
01
-20
14
02
-20
14
03
-20
14
Mo
istu
re C
on
ten
t [%
]
MC-FULL-S-CONT MC-FULL-S-312 MC-FULL-S-412
MC-FULL-S-612 EMC (1 wk)
Seasonal Roof Sheathing Moisture Contents
EMC calculated - Hailwood and Horrobin (1946)
0
5
10
15
20
25
300
9-2
01
2
10
-20
12
11
-20
12
12
-20
12
01
-20
13
02
-20
13
03
-20
13
04
-20
13
05
-20
13
06
-20
13
07
-20
13
08
-20
13
09
-20
13
10
-20
13
11
-20
13
12
-20
13
01
-20
14
02
-20
14
03
-20
14
Mo
istu
re C
on
ten
t [%
]
MC-FULL-N-CONT MC-FULL-N-312 MC-FULL-N-412
MC-FULL-N-612 EMC (1 wk)
Seasonal Average Moisture Contents
0
5
10
15
20
25
30
Fall 2012 Winter2012/2013
Spring 2013 Summer2013
Fall 2013 Winter2013/2014
Spring 2014
Mo
istu
re C
on
ten
t (%
)
MC-FULL-N-CONT MC-FULL-S-CONT MC-FULL-N-312 MC-FULL-S-312
MC-FULL-N-412 MC-FULL-S-412 MC-FULL-N-612 MC-FULL-S-612
Long Term Impacts of Elevated Moisture Contents
North 3:12 after 1 yr North 4:12 after 1 yr
Tracking Mold Growth
TABLE 2: VITTANEN’S MOLD GROWTH INDEX DESCRIPTIONS
INDEX GROWTH RATE DESCRIPTION
0 No growth Spores not activated
1 Small amounts of mold on surface (microscope) Initial stages of growth
2 <10% coverage of mold on surface (microscope) ___
3 10% – 30% coverage of mold on surface (visual) New spores produced
4 30% – 70% coverage of mold on surface (visual) Moderate growth
5 >70% coverage of mold on surface (visual) Plenty of growth
6 Very heavy and tight growth Coverage around 100%
Tracking Mold Growth – Year 1
Why is the Sheathing Wet? What is the Mechanism?
Night sky condensation!
Radiative heat loss from roof
surface to colder night sky
When Does it Occur?
When Does it Occur?
0
100
200
300
400
500
600
700
800
900
1000
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Sola
r R
adia
tio
n [
W/m
2 ]
Solar Radiation CONDENSE-Plywood-312
Incr
eas
ing
Surf
ace
Co
nd
en
sati
on
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Mo
istu
re C
on
ten
t [%
] an
d T
em
pe
ratu
re [
°C]
Condensation
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Mo
istu
re C
on
ten
t [%
] an
d T
emp
erat
ure
[°C
]
MC-FULL-N-312 MC-IN-SURF-N-312 T-IN-N-312-Plywood
T-N-312-Embedded Outdoor - Temperature Outdoor - Dewpoint
COND-N-312 Sheathing Solar Radiation
Condensation
When Does it Occur on the Underside of the
Sheathing?
0
100
200
300
400
500
600
700
800
900
1000
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Sola
r R
adia
tio
n [
W/m
2 ]
Solar Radiation CONDENSE-Plywood-312
Incr
easi
ng
Surf
ace
Co
nd
ensa
tio
n
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Mo
istu
re C
on
ten
t [%
] an
d T
emp
era
ture
[°C
]
Condensation
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Mo
istu
re C
on
ten
t [%
] an
d T
emp
erat
ure
[°C
]
MC-FULL-N-312 MC-IN-SURF-N-312 T-IN-N-312-Plywood
T-N-312-Embedded Outdoor - Temperature Outdoor - Dewpoint
COND-N-312 Sheathing Solar Radiation
Condensation
0
100
200
300
400
500
600
700
800
900
1000
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Sola
r R
adia
tio
n [
W/m
2 ]
Solar Radiation CONDENSE-Plywood-312
Incr
eas
ing
Surf
ace
Co
nd
en
sati
on
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Mo
istu
re C
on
ten
t [%
] an
d T
em
pe
ratu
re [
°C]
Condensation
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Mo
istu
re C
on
ten
t [%
] an
d T
emp
erat
ure
[°C
]
MC-FULL-N-312 MC-IN-SURF-N-312 T-IN-N-312-Plywood
T-N-312-Embedded Outdoor - Temperature Outdoor - Dewpoint
COND-N-312 Sheathing Solar Radiation
Condensation
0
100
200
300
400
500
600
700
800
900
1000
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Sola
r R
adia
tio
n [
W/m
2 ]
Solar Radiation CONDENSE-Plywood-312
Incr
eas
ing
Surf
ace
Co
nd
en
sati
on
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Mo
istu
re C
on
ten
t [%
] an
d T
em
pe
ratu
re [
°C]
Condensation
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Mo
istu
re C
on
ten
t [%
] an
d T
emp
erat
ure
[°C
]
MC-FULL-N-312 MC-IN-SURF-N-312 T-IN-N-312-Plywood
T-N-312-Embedded Outdoor - Temperature Outdoor - Dewpoint
COND-N-312 Sheathing Solar Radiation
Condensation
Dry
Heavy Condensation
Light Condensation
Daily Solar Radiation Cycles
Some Nuances of Condensation on Plywood
Nuances of Mold Growth on Plywood Heartwood vs Sapwood
Monitoring Night Sky Cooling Impacts
Shingle & Sheathing Temperature Depressions –
Night Sky Cooling
2.6 2.5 2.52.6
2.4 2.5
0.9 0.9 0.9 1.0 1.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
312-N 312-S 412-N* 412-S 612-N 612-S
Tem
pe
ratu
re D
epre
ssio
n f
rom
Am
bie
nt
(°C
)
Avg Shingle T Avg Interior Sheathing Surface T
*412-N sheathing temperature unavailable due to sensor malfunction
4.5°FOn top of shingles
<2°FAt interior of roof sheathing
Average Shingle and Sheathing Temperature Depression compared to Ambient
Temperature for Winter (December 1, 2013 to January 31, 2014).
Hours of Potential Condensation - Sheathing
0
100
200
300
400
500
600
700
800
0.00
0.25
0.50
0.75
1.00
1.25
1.50
North South
Ho
urs
of
Po
ten
tial
Co
nd
en
sati
on
Tem
pe
ratu
e D
ep
ress
ion
fro
m A
mb
ien
t (°
C)
3:12 Temp 4:12 Temp 6:12 Temp 3:12 Hours 4:12 Hours 6:12 Hours
<2°F temperature drop
150 to 300 hours per year
On the Flip Side: Solar Heat Gain & Drying during the
Day
On the Flip Side: Solar Heat Gain & Drying Potential
0
5
10
15
20
25
30
35
40
45
50
55
60
Aug 21 00:00 Aug 21 06:00 Aug 21 12:00 Aug 21 18:00 Aug 22 00:00
Tem
pe
ratu
re [
°C]
Temperatures - 3:12 and 6:12 Slope Roofs - Early Spring Conditions
T-OUT-N-612-Shingle
T-OUT-S-612-Shingle
T-IN-N-612-Plywood
T-IN-S-612-Plywood
T-OUT-N-312-Shingle
T-OUT-S-312-Shingle
T-IN-N-312-Plywood
T-IN-S-312-Plywood
Outdoor - Dewpoint
Outdoor - Temperature
South Shingles
130 -140°F
North Shingles
100-110°F
Ambient Air
up to 79°F
South Sheathing = 98°F
North Sheathing = 90°F
Shingle and Sheathing Temperature Rise – During the
Winter
1.9
5.8
1.7
6.5
1.7
6.6
0.9
1.7
0.9
2.01.7 1.8
0
1
2
3
4
5
6
7
312-N 312-S 412-N 412-S 612-N 612-S
Tem
pe
ratu
re R
ise
Fro
m A
mb
ien
t (°C
)
Avg Shingle T Avg Interior Sheathing Surface T
Shingle Surface
Sheathing
~11°F
~4°F
Impact of Impermeable SAM vs Permeable Roofing
Felt Underlay
0
5
10
15
20
25
30
Oct 17 Nov 14 Dec 12 Jan 09 Feb 06 Mar 06 Apr 03 May 01 May 29 Jun 26
Mo
itsu
re C
on
ten
t (%
)
MC-OUT-S-CONT MC-OUT-S-312
South Slope - Fall to Spring
Impermeable SAM vs Permeable Roofing Felt Underlay
0
5
10
15
20
25
30
Oct 17 Nov 14 Dec 12 Jan 09 Feb 06 Mar 06 Apr 03 May 01 May 29 Jun 26
Mo
itsu
re C
on
ten
t (%
)
MC-OUT-N-CONT MC-OUT-N-312
Permeable Felt
Impermeable SAM
North Slope - Fall to Spring
Okay But.. What Happens when Shingles Start to
Leak/Seep - Long Term?
Key Findings – The Cause of the Problem in the
Pacific Northwest
Roof sheathing in well ventilated attics (also soffits, canopies)
experiences elevated moisture levels in winter
Occurs despite elimination of typical wetting mechanisms within
attics (air leakage, duct leakage, rain water leaks etc.)
Moisture level is above equilibrium level indicating additional wetting
sources
Night sky cooling causes wetting when sheathing drops below ambient
dewpoint (few hundred hours per year) in attic
Difficult to stop it from occurring
Fungal growth occurs due elevated moisture and condensation on
underside of sheathing
More fungal growth on north than south – drying matters, the heat
from a ceiling above a house will also help too
Monitoring of Potential Mitigation Strategies
Vented underlayment – de-
couple night sky radiation
cooling effects
Surface treatments to kill &
prevent fungal growth
Night Sky Radiation De-Coupler?
Vented shingle underlay
installed in one roof in 2nd year
of study
Purpose: try to de-couple
night sky cooling effects
from sheathing
Vented Underlay – The Double Edged Sword
South Orientation – Vented Underlay vs Direct Applied Shingles
0
50
100
150
200
250
300
350
400
450
-5
0
5
10
15
20
25
Jan 16 Jan 17 Jan 18
Sola
r R
adia
tio
n (
W/m
2 )
Tem
per
atu
re (
°C)
T-OUT-S-VENT (Shingles) T-IN-S-VENT (Sheathing)
T-OUT-S-312 (Shingles) T-IN-S-312 (Sheathing)
Outdoor T T-Drainmat-S-VENT
Solar Radiation
Shingles – direct applied
Shingles – vent mat
12°F drop in
shingle
3°F drop in
sheathing
Vented Underlay – The Double Edged Sword
0
2
4
6
8
10
12
14
16
6
8
10
12
14
16
18
20
22
Day Night Avg
Tem
per
atu
re (
°C)
Mo
istu
re C
on
ten
t (%
)
Spring
VENT-N-MC VENT-S-MC 312-N-MC 312-S-MC
VENT-N-T VENT-S-T 312-N-T 312-S-T
Vent Normal
No
rth
Sou
th
No
rth
Sou
th
Spring (March 1, 2013 to April 30, 2013) Diurnal Moisture Content (SURF)
and Temperature Averages for North and South Oriented Vented and
Control (Direct Applied Shingles) Roof Assemblies
Round 1 - Surface Treatment Application
4 huts x 2 orientations = 8
applications of each
Fungicides, Cleaners, Sealers
› Boracol® 20-2
› Boracol® 20-2 BD
› Bleach
› Thompson’s WaterSeal®
› Kilz® Paint
Wood Preservatives
› Copper Naphthenate
› Zinc Naphthenate
Wood Preservative & Fungicide Surface Treatments
When Applied 1 Year Later
Fungal Growth observed is Cladosporium
North vs South Orientation
Visual Assessment of Surface Treatment Efficacy
VISUAL ASSESSMENT OF SURFACE TREATMENT EFFICACY
Test
Roof
Surface Treatments (north left, south right)
San
sin
Bo
raco
l®
20
-2
Co
pp
er
Nap
hth
en
ate
Ble
ach
Th
om
pso
ns
Wate
rSe
al
®
Kil
z®
Pain
t
Zin
c
Nap
hth
en
ate
San
sin
Bo
raco
l®
20
-2B
D
Control
3:12
4:12
6:12
VISUAL ASSESSMENT SCALE
Prist ine or very light fungal growth
Moderate fungal growth
Signif icant fungal growth
Hence need for duplicate samples – slope not a big factor (heartwood vs sapwood is)
In our experience Kilz® & Boracol® 20-
2BD while okay here after 2 years may
not be best long term for fungal growth
Wood Preservative & Fungicide Surface Treatments
The best decay fungicide (Boracol 20-2BD) & surface
paint (Kilz) looked okay in years 1 and 2 – but not in year
3
A Caution with Surface Treatments
A Caution with Surface Treatments
A Caution with Surface Treatments
Summary – Mitigation Strategy Performance
Thermally de-coupling the exposed shingles from the sheathing did
not work well
Did not significantly “warm” sheathing temperature at night
On flip-side – the sheathing did not get as hot during the day, so
less drying and resulting prolonged wet periods
Surface treatments appear to be a potential viable solution if right
product is developed - current products not quite effective (nor
developed specifically for this application)
Concurrent work by FP to perform accelerated testing of some new
biocides/fungicides
Ongoing monitoring at our huts to monitor long-term field
performance of next generation treatments
Concurrent Fungicide/Biocide Research –
FP Innovations
Images courtesy FP Innovations
Developed an
accelerated 12 week test
method to evaluate new
fungicides applied to
wood products
Have already tested a
handful of newly
innovated & proprietary
fungicides & coatings
A few promising
formulations completely
prevented mold growth
Follow-up with field
testing
Round 2 - Field Trials & Monitoring of New Surface
Treatments
Nine New Treatments Applied to Both Cleaned &
Moldy Sheathing
Adapting Surface Treatments for the Field (Underside
Application)
Ongoing Monitoring of New Surface Treatments
Most Promising
fungicide/biocide is
water repelling &
contains several “active”
ingredients to prevent
long term mold growth.
Note it is not a wood
preservative it is a
fungicide
Currently undergoing
environmental testing &
available soon?
What A Real Roof Leak Ends up Doing to Sheathing
(6 Months)
Final Thoughts
Ventilated attics & roof assemblies ‘built to code’ are experiencing
mold growth on underside of sheathing (plywood or OSB)
Wetting from night sky condensation and may be exacerbated
by air leaks & water leaks
Hard to reliably stop night sky condensation
More ventilation makes it worse, less may also
Mold growth may be minor but perceived as risk
Could build other attic assemblies but unlikely to replace
ventilated attics any time soon
Need to address durability & sensitivity of wood based sheathings
to mold growth
Just make sure the fungicide is no more harmful to humans
that the mold is
