The document discusses the performance of ventilated attics, highlighting key problems related to moisture issues caused by factors such as air leakage, inadequate ventilation, and outdoor moisture sources like night sky condensation. A case study is presented that illustrates typical attic complications and remediation strategies, including air sealing and surface treatments to manage mold growth. The findings emphasize that elevated moisture in attics often exceeds the drying capacity provided by ventilation, necessitating effective design and maintenance practices.

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Attics: Problems and Solutions
BOABC FALL EDUCATION CONFERENCE
November 16, 2016
Presented by: Lorne Ricketts | MASc, P.Eng.

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 Ventilated Attic Performance
 Case Study
 Attic Roof Hut Research
 In Search of Solutions
 Summary
Presentation Overview

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An Obvious Problem

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A Not So Obvious Problem

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Factors Affecting 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…

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Where are we Seeing the Biggest Issues?
1. Air leakage (ceiling details)
2. Exhaust duct leaks & discharge location (roof, soffit, or wall)
3. Inadequate venting provisions (amount, vent location, or materials)
4. Outdoor moisture: night sky condensation on underside of sheathing
5. Wetting through shingles/roofing (tipping the moisture balance)

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The Localized Nature of Air Leakage Condensation

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Standard Faith-Based Air-Sealing Approach
Air-sealing details, duct exhaust
details often not provided & left
up to the contractor

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The Localized Nature of Leaking Penetrations

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Typical Issues – Impact of Orientation
South Facing
North Facing

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Typical Issues – Impact of Orientation
North =
Soaked
South (Partially
Shaded) = Damp

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Influence of Solar Radiation & Night Sky Radiation

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The Nature of Outdoor Moisture Wetting &
Night Sky Condensation

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Other Not So Great Ideas…

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It Happens in Ventilated Low Slope & Cathedral Ceilings Too

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So When Does it Become a Problem?

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So When Does it Become a Problem?

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So When Does it Become a Problem?

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Case Study: Two Steps Forward, One Step Backwards
 2007 investigation of 5 year old large townhouse complex
 Was experiencing many of the typical attic problems

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An Assortment of Issues – Exhaust Duct Details

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An Assortment of Issues – Exhaust Duct Details

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An Assortment of Issues – Inadequate Ridge ‘Vent’ Material
Almost no effective net
free area, 5 layers of filter
fabric

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An Assortment of Issues – Ceiling Air Leakage

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Attic Remediation (2 Years Later)

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Full Review of Initial Contributing Factors - Air-Sealing

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Retrofit Ceiling Air Sealing - Sprayfoam

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Ceiling Air Sealing – Poly Bags of Fun...

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New Exhaust Vent Hoods & Attic Ridge Vents

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Mold Remediation - Dry Ice Blasting

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2 years after remediation...

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Water Leaks Around Plugged Dryer Exhaust Ducts

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Lack of Dryer Exhaust Duct Maintenance

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Soffit Exhaust Vent Hood Configuration Issues

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Air-Sealing Issues

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Air-Sealing Issues

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But we know how to solve these problems...
Guide to Best Practices for Air Sealing and
Insulation Retrofits - Produced by RDH and published
by BC Housing

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Effectiveness of Dry Ice Blasting against Mold?

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Water Seepage through Aged & Saturated Asphalt Shingles?

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General Mold Growth Not Attributable to Typical Sources

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Measuring the Wetting

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Key Findings from Field Investigations
 Seeing widespread issues with
mold growth in wood-frame attics in
Coastal Pacific Northwest in past
decade
 Wetting 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)

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Field Monitoring Study

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Industry Trends – Less Heat Flow into 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

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Research Study
 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 Theoretical attic with no air
leakage or heat loss into
the attic and unrestricted
ventilation
(Arrangement for Study)
Typical ventilated attic
construction with air
leakage and heat loss into
the attic

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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

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Roof Test Hut Field Monitoring Setup

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Monitoring Equipment & Sensors
Moisture Content, Temperature, Relative
Humidity and surface Condensation sensors –
north and south slopes x 4 huts

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Results – Long Term Roof Sheathing Moisture Contents
0
5
10
15
20
25
30
09-2012
10-2012
11-2012
12-2012
01-2013
02-2013
03-2013
04-2013
05-2013
06-2013
07-2013
08-2013
09-2013
10-2013
11-2013
12-2013
01-2014
02-2014
03-2014
MoistureContent[%]
MC-FULL-S-CONT MC-FULL-S-312 MC-FULL-S-412
MC-FULL-S-612 EMC (1 wk)

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Results - Seasonal Averages
0
5
10
15
20
25
30
Fall 2012 Winter
2012/2013
Spring 2013 Summer
2013
Fall 2013 Winter
2013/2014
Spring 2014
MoistureContent(%)
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

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Long-Term Impacts of Elevated Moisture Contents
North 3:12 after 1 year North 4:12 after 1 year

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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%

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Tracking Mold Growth – Year 1

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Why is the Sheathing Wet? What is the Mechanism?
 Night sky condensation!
(Important: It happen when all moisture sources eliminated.)
Radiative heat loss from roof surface
to colder night sky

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When Does it Occur?

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When Does it Occur?
0
100
200
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
S
Solar Radiation CONDENSE-Plywood-312
Increa
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
MoistureContent[%]andTemperature[°C]
Condensation
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
MoistureContent[%]andTemperature[°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

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Monitoring Night Sky Cooling Impacts

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When Does it Occur?
0
100
200
300
400
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
SolarR
Solar Radiation CONDENSE-Plywood-312
IncreasingSu
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
MoistureContent[%]andTemperature[°C]
Condensation
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
MoistureContent[%]andTemperature[°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
SolarRadiation[W/m2]
Solar Radiation CONDENSE-Plywood-312
IncreasingSurfaceCondensation
20
25
30
mperature[°C]
20
25
30
emperature[°C]
0
100
200
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
Solar Radiation CONDENSE-Plywood-312
Inc
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
MoistureContent[%]andTemperature[°C]
Condensation
0
5
10
15
20
25
30
Oct 02 Oct 03 Oct 04 Oct 05 Oct 06
MoistureContent[%]andTemperature[°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
Heavy Condensation
Daily Solar Radiation
Cycles
Dry
Light Condensation

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Shingle & Sheathing Temperature Depressions
2.6 2.5 2.5
2.6
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
TemperatureDepressionfromAmbient
(°C)
Avg Shingle T Avg Interior Sheathing Surface T
*412-N sheathing temperature unavailable due to sensor malfunction
Average Shingle and Sheathing Temperature Depression compared to
Ambient Temperature for Winter
(December 1, 2013 to January 31, 2014).

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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
HoursofPotentialCondensation
TemperatueDepressionfromAmbient(°C)
3:12 Temp 4:12 Temp 6:12 Temp 3:12 Hours 4:12 Hours 6:12 Hours
150 to 300 hours per year

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Nuances of Mold on Plywood - Heartwood vs Sapwood

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On the Flip Side: Solar Heat Gain & Drying During the Day

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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
Temperature[°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 55°C
North Shingles
35-40°C
South Sheathing = 35°C
North Sheathing = 31°C
Ambient
Air up to
21°C
Lots of cloud cover changes the wetting and drying balance.

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A Localized Problem...
Seattle
Portland
Vancouver
San Francisco
Calgary
High Risk Climate for
Night Sky Radiation Attic
Moisture Issues

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Key Findings – The Cause of the Pacific Northwest Problems
 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 to elevated moisture content and condensation on
underside of sheathing
 More fungal growth on north than south – drying matters, the heat from a ceiling
above a house will help too

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Monitoring of Potential Mitigation Strategies
 Vented underlayment to
de-couple night sky radiation
cooling effects
 Surface treatments to kill &
prevent fungal growth

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Vented Underlay - 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

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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
SolarRadiation(W/m2)
Temperature(°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
6°C drop in
shingle
1°C drop in
sheathing

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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
Temperature(°C)
MoistureContent(%)
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
North
South
North
South
Vent Normal
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

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Surface Treatment Application – Round 1
 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

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Wood Preservative & Fungicide Surface Treatments
When Applied 1 Year Later
Fungal Growth observed is Cladosporium

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North vs South Orientation
South North

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Visual Assessment of Surface Treatment Efficacy
VISUAL ASSESSMENT OF SURFACE TREATMENT EFFICACY
Test
Roof
Surface Treatments (north left, south right)
Sansin
Boracol®
20-2
Copper
Naphthenate
Bleach
Thompsons
WaterSeal®
Kilz®Paint
Zinc
Naphthenate
Sansin
Boracol®
20-2BD
Control
3:12
4:12
6:12
VISUAL ASSESSMENT SCALE
Pristine or very light fungal growth
Moderate fungal growth
Significant fungal growth
In our experience Kilz® & Boracol® 20-
2BD while okay here after 2 years may
not be best long term for fungal growth
Need duplicate samples – slope not a big factor (heartwood vs
sapwood is)

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Wood Preservative & Fungicide Surface Treatments
The best decay fungicide looked okay in years 1 and
2 – but not in year 3

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A Caution with Surface Treatments

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A Caution with Surface Treatments

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A Caution with Surface Treatments

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Summary – Mitigation Strategy Performance
 Thermally de-coupling the exposed shingles from the sheathing did
not work well
 Did not significantly increase sheathing temperature at night, but did
reduce drying from solar heat gain
 Surface treatments appear to be a potentially viable solution if right
product is developed – currently available products not quite
effective (nor developed specifically for this application)
 Concurrent work by FP Innovations to perform accelerated testing of
some new biocides/fungicides
 Ongoing monitoring of huts to monitor long-term field performance of
next generation treatments

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Concurrent Fungicide/Biocide Research – 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
Images courtesy FP Innovations

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Field Trials & Monitoring of 9 New Treatments – Round 2

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Adapting Surface Treatments for Underside Application

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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?

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Relative Risk of Wood-Frame Roof Assemblies

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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
 Ventilation on its own is not a solution
 Mold growth may be minor but perceived as risk
 Could build other roof assemblies but unlikely to replace ventilated attics
any time soon
 Need to address durability & sensitivity of wood based sheathings to mold
growth, various groups are developing products
 Just make sure the fungicide is no more harmful to humans than the
mold is…

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Additional Resources
RDH Technical Bulletin No. 10 - Mold in Vented
Wood-Frame Roofs in the Coastal Pacific Northwest
RDH Blog Article – Re-Thinking Ventilated Attics:
How to Stop Mold Growth in Coastal Climates
Why Wood Frame Attics Get Wet & Mouldy in the
Pacific Northwest - Conference Paper at 30th RCI
International Convention & Tradeshow
Guide to Best Practices for Air Sealing and
Insulation Retrofits - Produced by RDH and published
by BC Housing

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FOR FURTHER INFORMATION PLEASE VISIT
 www.rdh.com and www.buildingsciencelabs.com
 Lorne Ricketts - lricketts@rdh.com
Discussion + Questions