the problems with and solutions for ventilated attics
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The Problems With and Solutions for Ventilated Attics RCI 30TH INTERNATIONAL CONVENTION - SAN ANTONIO, TX MARCH 9, 2015
GRAHAM FINCH, MASC, P.ENG – RDH BUILDING ENGINEERING LTD.
Presentation Overview
à Current Issues with Ventilated Attics
à Case Study of Repairs
à Attic Roof Hut Research & Monitoring Study – Key Findings
à Performance of Potential Solutions
à 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?
à Roof orientation (solar radiation)
à Roof slope (solar radiation)
à Roofing material/color
à Adjacent buildings – shading
à Trees – shading & debris
à Outdoor climate
à Indoor climate
à Roof Leaks
à Insulation R-value
à Air leakage from house
à Duct leakage in attic
à Duct discharge location
à Vent area and distribution
à Sheathing durability
à Roof maintenance
à 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 o4en not provided & le4 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
South Facing
North Facing
Typical Issues – Impact of Orientation
North = Soaked
South (Par?ally 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
à Seeing widespread issues with mold growth in newer wood-frame attics in Pacific Northwest
à Wetting is exceeding drying capacity provided by ventilation
à Problem is most often NOT due to a lack of ventilation
à Usual culprits of air-leakage condensation (leaky ceiling, leaky ducts & discharge point)
à Also seeing supplemental exterior moisture sources (night sky condensation, rainwater seepage)
Field Monitoring Study
Research Study Premise
à Controlled field monitoring study to isolate exterior wetting mechanisms from interior sources (air, vapour)
à To specifically evaluate impact of orientation, slope (3:12, 4:12 and 6:12) & shingle underlay
à Remove influence of air leakage or heat gain from house
à 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
à Homeowner Protection Office of BC
à RDH – monitoring field conditions & controlled field study (covered here)
à MH – monitoring of attic moisture levels and air-leakage from indoors into attic spaces
à FP Innovations – monitoring of effectiveness of various surface treatments
à 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
3009
-‐201
2
10-‐201
2
11-‐201
2
12-‐201
2
01-‐201
3
02-‐201
3
03-‐201
3
04-‐201
3
05-‐201
3
06-‐201
3
07-‐201
3
08-‐201
3
09-‐201
3
10-‐201
3
11-‐201
3
12-‐201
3
01-‐201
4
02-‐201
4
03-‐201
4
Moisture Co
nten
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
3009
-‐201
2
10-‐201
2
11-‐201
2
12-‐201
2
01-‐201
3
02-‐201
3
03-‐201
3
04-‐201
3
05-‐201
3
06-‐201
3
07-‐201
3
08-‐201
3
09-‐201
3
10-‐201
3
11-‐201
3
12-‐201
3
01-‐201
4
02-‐201
4
03-‐201
4
Moisture Co
nten
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
Moisture Co
nten
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?
à 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
Solar R
adiatio
n [W
/m2 ]
Solar Radiation CONDENSE-‐Plywood-‐312
Increasing
SurfaceCo
nden
satio
n
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Moisture Co
nten
t [%] a
nd Tem
perature [°C]
Condensation
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Moisture Co
nten
t [%] a
nd Tem
perature [°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
Solar R
adiatio
n [W
/m2 ]
Solar Radiation CONDENSE-‐Plywood-‐312
Increasing
SurfaceCo
nden
satio
n
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Moisture Co
nten
t [%] a
nd Tem
perature [°C]
Condensation
0
100
200
300
400
500
600
700
800
900
1000
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Solar R
adiatio
n [W
/m2 ]
Solar Radiation CONDENSE-‐Plywood-‐312
Increasing
SurfaceCo
nden
satio
n
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Moisture Co
nten
t [%] a
nd Tem
perature [°C]
Condensation
0
100
200
300
400
500
600
700
800
900
1000
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Solar R
adiatio
n [W
/m2 ]
Solar Radiation CONDENSE-‐Plywood-‐312
Increasing
SurfaceCo
nden
satio
n
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Moisture Co
nten
t [%] a
nd Tem
perature [°C]
Condensation
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Moisture Co
nten
t [%] a
nd Tem
perature [°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 Condensa.on
Light Condensa.on Daily Solar Radia.on 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-‐STempe
rature Dep
ression from
Ambien
t (°C)
Avg Shingle T Avg Interior Sheathing Surface T
*412-‐N sheathing temperature unavailable due to sensor malfunction
4.5°F On top of shingles
<2°F At 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
Hours o
f Poten
tial C
onde
nsation
Tempe
ratue De
pression
from
Ambien
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
Tempe
rature [°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
Tempe
rature Rise From Ambien
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
Moitsure Co
nten
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
Moitsure Co
nten
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
à Roof sheathing in well ventilated attics (also soffits, canopies) experiences elevated moisture levels in winter
à Occurs despite elimination of typical wetting mechanisms within attics (air leakage, duct leakage, rain water leaks etc.)
à Moisture level is above equilibrium level indicating additional wetting sources
à Night sky cooling causes wetting when sheathing drops below ambient dewpoint (few hundred hours per year) in attic
à Difficult to stop it from occurring
à Fungal growth occurs due elevated moisture and condensation on underside of sheathing
à 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
à Vented underlayment – de-couple night sky radiation cooling effects
à Surface treatments to kill & prevent fungal growth
Night Sky Radiation De-Coupler?
à Vented shingle underlay installed in one roof in 2nd year of study
à 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
050100150200250300350400450
-‐5
0
5
10
15
20
25
Jan 16 Jan 17 Jan 18
Solar R
adiatio
n (W
/m2 )
Tempe
rature (°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
Tempe
rature (°C)
Moisture Co
nten
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
North
South
North
South
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
à 4 huts x 2 orientations = 8 applications of each
à Fungicides, Cleaners, Sealers
› Boracol® 20-2
› Boracol® 20-2 BD
› Bleach
› Thompson’s WaterSeal®
› Kilz® Paint
à 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)
Sansi
n
Bora
col®
20-2
Copper
N
aphth
enat
e
Ble
ach
Thom
pso
ns
Wat
erSe
al ®
Kilz® P
aint
Zin
c N
aphth
enat
e
Sansi
n
Bora
col®
20-2
BD
Control
3:12
4:12
6:12
VISUAL ASSESSMENT SCALE
Pristine or very light fungal growth
Moderate fungal growth
Significant 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
à Thermally de-coupling the exposed shingles from the sheathing did not work well
à Did not significantly “warm” sheathing temperature at night
à On flip-side – the sheathing did not get as hot during the day,
so less drying and resulting prolonged wet periods
à 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)
à Concurrent work by FP to perform accelerated testing of some new biocides/fungicides
à 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
à Developed an accelerated 12 week test method to evaluate new fungicides applied to wood products
à Have already tested a handful of newly innovated & proprietary fungicides & coatings
à A few promising formulations completely prevented mold growth
à 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
à Ventilated attics & roof assemblies ‘built to code’ are experiencing mold growth on underside of sheathing (plywood or OSB)
à Wetting from night sky condensation and may be exacerbated by air leaks & water leaks
à Hard to reliably stop night sky condensation
à More ventilation makes it worse, less may also
à Mold growth may be minor but perceived as risk
à Could build other attic assemblies but unlikely to replace ventilated attics any time soon
à Need to address durability & sensitivity of wood based sheathings to mold growth
à Just make sure the fungicide is no more harmful to humans that the mold is
à rdh.com
Discussion + Questions
Graham Finch – gfinch@rdh.com – 604-873-1181
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