The Problem With and Solutions for Ventilated Attics

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?



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


Mo

istu

re C

on

ten

t [%

] an

d T

em

pe

ratu

re [

°C]

Condensation

0

5

10

15

20

25

30


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


Sola

r R

adia

tio

n [

W/m

2 ]


Incr

easi

ng

Surf

ace

Co

nd

ensa

tio

n

0

5

10

15

20

25

30


Mo

istu

re C

on

ten

t [%

] an

d T

emp

era

ture

[°C

]

Condensation

0

5

10

15

20

25

30


Mo

istu

re C

on

ten

t [%

] an

d T

emp

erat

ure

[°C

]




Condensation

0

100

200

300

400

500

600

700

800

900

1000


Sola

r R

adia

tio

n [

W/m

2 ]


Incr

eas

ing

Surf

ace

Co

nd

en

sati

on

0

5

10

15

20

25

30


Mo

istu

re C

on

ten

t [%

] an

d T

em

pe

ratu

re [

°C]

Condensation

0

5

10

15

20

25

30


Mo

istu

re C

on

ten

t [%

] an

d T

emp

erat

ure

[°C

]




Condensation

0

100

200

300

400

500

600

700

800

900

1000


Sola

r R

adia

tio

n [

W/m

2 ]


Incr

eas

ing

Surf

ace

Co

nd

en

sati

on

0

5

10

15

20

25

30


Mo

istu

re C

on

ten

t [%

] an

d T

em

pe

ratu

re [

°C]

Condensation

0

5

10

15

20

25

30


Mo

istu

re C

on

ten

t [%

] an

d T

emp

erat

ure

[°C

]




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



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

rdh.com

Discussion + Questions

Graham Finch – [email protected] – 604-873-1181

The Problem With and Solutions for Ventilated Attics

Engineering