The Problems With and Solutions for Ventilated Attics

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

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

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

The Localized Nature of Wetting

Water Leaks Around Plugged Dryer Exhaust Ducts

Lack of Dryer Exhaust Duct Maintenance

Soffit Exhaust Vent Hood Configuration 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)

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

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
Moisture
Content
[%]

MC-‐FULL-‐S-‐CONT
MC-‐FULL-‐S-‐312

MC-‐FULL-‐S-‐612 EMC
(1
wk)
Seasonal Roof Sheathing Moisture Contents
EMC calculated - Hailwood and Horrobin (1946)
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
Moisture
Content
[%]

MC-‐FULL-‐N-‐CONT
MC-‐FULL-‐N-‐312

MC-‐FULL-‐N-‐612 EMC
(1
wk)

Seasonal Average Moisture Contents
0
5
10
15
20
25
30
Fall
2012 Winter
2012/2013
Spring
2013 Summer
2013
Fall
2013 Winter
2013/2014
Spring
2014
Moisture
Content
(%)

MC-‐FULL-‐N-‐CONT
MC-‐FULL-‐S-‐CONT


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?
0
100
200
300
Oct
02 Oct
03 Oct
04 Oct
05 Oct
06
Sol
Solar
Radiation
CONDENSE-‐Plywood-‐312
Increasin
0
5
10
15
20
25
30
Oct
02 Oct
03 Oct
04 Oct
05 Oct
06
Moisture
Content
[%]
and
Temperature
[°C]
Condensation
0
5
10
15
20
25
30
Oct
02 Oct
03 Oct
04 Oct
05 Oct
06
Moisture
Content
[%]
and
Temperature
[°C]

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
Oct
02 Oct
03 Oct
04 Oct
05 Oct
06
Solar
Rad
Solar
Radiation
IncreasingSurf
0
5
10
15
20
25
30
Oct
02 Oct
03 Oct
04 Oct
05 Oct
06
Moisture
Content
[%]
and
Temperature
[°C]
Condensation
0
100
200
300
400
500
600
700
800
900
1000
Oct
02 Oct
03 Oct
04 Oct
05 Oct
06
Solar
Radiation
[W/m2]
Solar
Radiation
IncreasingSurfaceCondensation
25
30
perature
[°C]
0
100
200
Oct
02 Oct
03 Oct
04 Oct
05 Oct
06
Solar
Radiation
Incre
0
5
10
15
20
25
30
Oct
02 Oct
03 Oct
04 Oct
05 Oct
06
Moisture
Content
[%]
and
Temperature
[°C]
Condensation
0
5
10
15
20
25
30
Oct
02 Oct
03 Oct
04 Oct
05 Oct
06
Moisture
Content
[%]
and
Temperature
[°C]

MC-‐IN-‐SURF-‐N-‐312
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 2.5
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
Temperature
Depression
from
Ambient

(°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
of
Potential
Condensation
Temperatue
Depression
from
Ambient
(°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
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-‐S-‐612-‐Plywood

T-‐OUT-‐N-‐312-‐Shingle

T-‐OUT-‐S-‐312-‐Shingle


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
2.0
1.7 1.8
0
1
2
3
4
5
6
7
312-‐N 312-‐S 412-‐N 412-‐S 612-‐N 612-‐S
Temperature
Rise

From
Ambient
(°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
Content
(%)

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
Content
(%)

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
0
50
100
150
200
250
300
350
400
450
-‐5
0
5
10
15
20
25
Jan
16 Jan
17 Jan
18
Solar
Radiation
(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
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
Temperature
(°C)
Moisture
Content
(%)
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

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
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

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

The Problems With and Solutions for Ventilated Attics

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