Selected findings of an IRC study of the wetting and drying potentials of wood-frame walls exposed to different climates

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Selected findings of an IRC study of the wetting and drying potentials

of wood-frame walls exposed to different climates

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Selected findings of an IRC study of the wetting and drying

potentials of wood-frame walls exposed to different climates

Rousseau, M.Z.; Dalgliesh, W.A.

ORAL-598

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1 Selected Findings of an IRC Study

of the Wetting and Drying Potentials

of Wood-Frame Walls

Exposed to Different Climates

byMadeleine Z Rousseau and W. Alan Dalgliesh

Institute for Research in Construction

Damage due to Rain Penetration

What is Too Wet for Too Long?

Minimizemoisture entry into the wall system, and

Maximizethe exit of moisture which does enter so that:

No component stays'too wet'for'too long‘

Systematic approach

to quantify too wet, too longfor woodin stud space and relative riskof its deterioration

associated with climate and wall assemblies characteristics

IRC Study - “MEWS”

•

Wood-frame wall assemblies

– Cladding system (masonry, stucco, EIFS, siding) • With/without an air space

– Sheathing board

– Insulation layer and location – Water resistive membrane – Vapour barrier

– Air leakage

•

North American climates

– Warm and wet (Wilmington NC) – Mild and wet (Seattle WA) – Cold and wet (Ottawa) – Cold and dry (Winnipeg) – Warm and dry (San Diego CA) – Hot and dry (Fresno) – Hot and dry (Phoenix Arizona)

Method in a nutshell

Climate characterisation

Model Simulation

hygIRC Output

Water ingress in specimens

Material properties Benchmarking --Climate Severity--> --Wal l Response--> Building practice

Wall with leaks into stud cavity Wall without leaks

Moisture Index RHT index

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MEWS Study: excessive RH and T

Outdoor climate Indoor climate

Materials, assembly and deficiencies

RH to be higher than

95%RHwhen Temp.

is above 5°C

?

Conditions conducive

to wood rot

•

Exterior climate severity

•

Deficiencies allowing water leakage in stud cavity

•

Properties of materials on the exterior – Cladding and installation on an open air space – Exterior insulation

– Sheathing board – Water resistive barrier

•

Properties of materials on the interior •Indoor climate

•Air leakage

Modelling Studies using hygIRC 2D

Effect of Climate Severity

MOISTURE INDEX ---> R H T I N D E X---> 0,0 BLUE - no leakage into assembly RED - water leakage into wall assembly

For porous & non-porous claddings

Water leakage into stud cavity

No leakage in stud cavity

Moisture loading due to climate increases

Duration of “too wet and too war m ” wal l cond it ions incre a ses

Effect of Water Leakage in Stud cavity

•

Severity of the climate

•

Type and size of deficiencies in the wall system, providing a path for water entry to the stud space

1 5 0 m m d ia m e te r v e n tila tio n d u c t

1 1 m m O S B

Joint Wall/Duct

Deficiency: missing seal

Magnitude of the moisture loads in the stud space depended on:

Pattern of Wall Response to Water Leakage in Stud Cavity

A

B

C

Moisture loads in the stud cavity (Q)

RHT(95) wal

l respon

se

Will vary with the wall assembly and the climate

Effect of Water Leakage in Stud Space

0 500 1000 1500 2000 2500 3000 3500 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Water Entry, % Q cu m m u lat ive RH T (9 5) Wilmington Seattle Ottawa Winnipeg San Diego Fresno Phoenix RHT95 for reference wall **08VS

RH &T Wall

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3

Effect of Water Leakage Loads into Stud Space

80 85 90 95 100 10 50 90 130 170 021 250 290 330 370 410 450 490 530 057 610 650 690 730 Time, days RH % 0 10 20 30 40 50 60 70 80 90 100 110 T , Q , d eci -L /m^ 2 WI8HS RH RH threshold 3296 WI8HS T T threshold Q, deci-L/m^2 LARGEmoisture loads in stud space - Wall A SMALLmoisture loads

in stud space - Wall A

Effect of Sheathing Property on RH & T Response

80 85 90 95 100 10 50 90 130 170 021 250 290 330 370 410 450 490 530 057 610 650 690 730 Time, days RH % 0 10 20 30 40 50 60 70 80 90 100 110 T, Q , de ci -L /m ^ 2 WI8HS RH RH threshold 3296 WI8HS T T threshold Q, deci-L/m^2

Sheathing board A Sheathing board B

85 90 95 100 10 50 90 13 0 17 0 21 0 25 0 29 0 33 0 37 0 41 0 45 0 49 0 53 0 57 0 61 0 65 0 69 0 73 0 Time, days RH % 0 10 20 30 40 50 60 70 80 90 100 110 T , Q, d eci-L /m^2 WIF16HS RH RH threshold 3337 WIF16HS T T threshold Q, deci-L/m^2

LARGEmoisture loading in stud cavity

A

B

C

RHT(95) wal

l respon

se

Drying to outside helped when leakage was small

Effect of Thermal Properties Outboard

Higher thermal resistance outboard increased the duration of Temp. above 5°C in all climates

40 45 50 55 60 65 70 75 80 85 90 95 100 10 50 90 130 170 021 250 290 330 370 410 450 490 530 057 610 650 690 730 Time, days RH % 0 5 10 15 20 25 T , Q , d eci-L /m ^ 2 WPx20vsXW4 RH RH threshold 1681 WPx20vsXW4 T T threshold Q, deci-L/m^2

Withinsulating layer outside Withoutinsulating layer outside

Effect of Cladding Properties

•

No effect on excessive RH (at or higher than 95%)

prevailing in stud space

•

One case of a stucco cladding wall exposed to severe climatic loads resulted in a small excessive RH load in stud space

Masonry STUCCO EIFS Lamina Siding Hardboard/ vinyl

Effect of Open Cavity Behind Cladding

•

Large positive effect observed when air space was coupled with a more vapour permeable sheathing board

•

When moisture loads in stud space were high, the drying potential of the vented cavity was not observed.

INT. EXT.

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Summing Up

9 Wetting of the stud cavity must be minimized, before benefits from drying strategies can kick in.

¾ Wetting from rain

¾ Condensation

¾ Water built-up during construction process

9 To reduce wetting from exterior sources:

9 ACCEPT 9 DEFLECT 9 COLLECT 9 DIRECT and 9 DON’T NEGLECT!

PRACTICE “SAFE” WALL!

To find out more …

Research reports and papers on the MEWS project :

9

Methodology

9

N. A. climate characterization

9

Hygrothermal properties of building materials

9

Laboratory evaluation of wall systems exposed to simulated wind-driven rain

9

Modelling results and benchmarking

9

Research team and industrial partners

Visit NRC website http://irc.nrc-cnrc.gc.ca/bes/mews/

Effect of Sheathing Property on RH & T Response

40 50 60 70 80 90 100 10 50 90 130 170 210 250 290 330 370 410 450 490 530 570 610 650 690 730 Time, days RH % 0 5 10 15 20 25 30 35 T , Q, d ec i-L /m ^2 FR8HS RH RH threshold 1112 FR8HS T T threshold Q, deci-L/m^2 40 50 60 70 80 90 100 10 50 90 130 170 021 250 290 330 370 410 450 490 530 057 610 650 690 730 Time, days RH % 0 5 10 15 20 25 30 35 T , Q , d eci-L /m^ 2 FRF16HS RH RH threshold 901 FRF16HS T T threshold Q, deci-L/m^2

SMALLmoisture loading in stud cavity