Attics: Problems and Solutions

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Attics: Problems and SolutionsBOABC FALL EDUCATION CONFERENCE

November 16, 2016Presented 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

sheathing5. 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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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

09-2

012

10-2

012

11-2

012

12-2

012

01-2

013

02-2

013

03-2

013

04-2

013

05-2

013

06-2

013

07-2

013

08-2

013

09-2

013

10-2

013

11-2

013

12-2

013

01-2

014

02-2

014

03-2

014

Moi

stur

e Co

nten

t [%

]

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 Winter2012/2013

Spring 2013 Summer2013

Fall 2013 Winter2013/2014

Spring 2014

Moi

stur

e 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

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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.)

Sub-cooling effect

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

300

400

500

600

700

800

900

1000

Oct 02 Oct 03 Oct 04 Oct 05 Oct 06

Sola

r Rad

iatio

n [W

/m2 ]

Solar Radiation CONDENSE-Plywood-312

Incr

easin

gSu

rfac

eCo

nden

satio

n

0

5

10

15

20

25

30


Moi

stur

e Co

nten

t [%

] and

Tem

pera

ture

[°C]

Condensation

0

5

10

15

20

25

30


Moi

stur

e Co

nten

t [%

] and

Tem

pera

ture

[°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

500

600

700

800

900

1000


Sola

r Rad

iatio

n [W

/m2 ]


Incr

easin

gSu

rfac

eCo

nden

satio

n

0

5

10

15

20

25

30


Moi

stur

e Co

nten

t [%

] and

Tem

pera

ture

[°C]

Condensation

0

100

200

300

400

500

600

700

800

900

1000


Sola

r Rad

iatio

n [W

/m2 ]


Incr

easin

gSu

rfac

eCo

nden

satio

n

0

5

10

15

20

25

30


Moi

stur

e Co

nten

t [%

] and

Tem

pera

ture

[°C]

Condensation

0

100

200

300

400

500

600

700

800

900

1000


Sola

r Rad

iatio

n [W

/m2 ]


Incr

easin

gSu

rfac

eCo

nden

satio

n

0

5

10

15

20

25

30


Moi

stur

e Co

nten

t [%

] and

Tem

pera

ture

[°C]

Condensation

0

5

10

15

20

25

30


Moi

stur

e Co

nten

t [%

] and

Tem

pera

ture

[°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 2.52.6

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-STem

pera

ture

Dep

ress

ion

from

Am

bien

t (°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

Hour

s of P

oten

tial C

onde

nsati

on

Tem

pera

tue

Depr

essio

n fr

om A

mbi

ent (

°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

Tem

pera

ture

[°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...

SeattlePortland

Vancouver

San Francisco

CalgaryHigh 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 tode-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

050100150200250300350400450

-5

0

5

10

15

20

25

Jan 16 Jan 17 Jan 18

Sola

r Rad

iatio

n (W

/m2 )

Tem

pera

ture

(°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 appliedShingles – 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

Tem

pera

ture

(°C)

Moi

stur

e 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

Nor

th

Sout

hN

orth

Sout

h

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) Sa

nsin

Bo

raco

l®

20-2

Copp

er

Naph

then

ate

Blea

ch

Thom

pson

s W

ater

Seal

®

Kilz

® Pa

int

Zinc

Na

phth

enat

e

Sans

in

Bora

col®

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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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 - [email protected]

Discussion + Questions

Engineering

Attics: Problems and Solutions