A Hygrothermal Analysis of International Timber Frame Wall Assemblies:

Tested Under Temperate Maritime Climatic Conditions

Lee CorcoranDublin School of Architecture

Dr. Aidan Duffy Sima Rouholamin

09.09.2013

• Percentage of housing units completed using timber frame construction in Ireland.

Introduction

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Source: ITFMA, 2004

to put this in context...

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Source: ITFMA, 2003

50%+ by 2011

Motivation

• Moisture problems have been identified as one of the major causes of building fabric failures.

• With timber, the potential for decay is heavily dependent on the presence of moisture or high Relative Humidity.

• Moisture related problems include:–Mould growth–Fungal decay

• Getting it wrong could lead to......

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photo: www.dspinspections.com

photo: Darren Berginphoto: Darren Bergin

photo: www.findingmoldexperts.com

Problem definition

The adoption of construction details that are not necessarily suitable for use in certain climates....

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Aims of the study

• Identify commonly used timber frame assemblies used on an international scale.

• Perform a hygrothermal analysis on the selected assemblies, under temperate maritime conditions.

• Assess the drying capacity of each wall assembly by modelling the stress of an additional moisture source.

• Identify the most suitable assembly for use in temperate maritime climates.

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Typical Timber Frame

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• Plasterboard with internal finish

• Vapour control layer

• Vertical/Horizontal timber members

• Insulation

• Sheathing board

• Breather membrane• Ventilated cavity

• External cladding

How does moisture enter our walls?

• Rain during the construction process.

• Poor detailing at junctions and openings.

• Specification of inappropriate materials at incorrect locations.

• Interstitial condensation due to temperature drops within the wall construction.

• Moisture from within the building can penetrate into the wall due to poor airtightness and service penetrations.

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Methodology Overview

• 4 wall assemblies were chosen for simulation based on a review of common international details.

• WUFI was used to carry out the hygrothermal simulations.

• Delphin was used as a means of partially verifying the WUFI hygrothermal model setup.• Climatic data: Dublin, Ireland (Design Reference Year)

• Time step: 1 hour

• Duration: 3 years• Additional moisture source modeled to test performance

under the stress of an additional moisture load.

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Wall AssembliesWall Types A+C* Wall Type B Wall Type D

*Wall Type C uses Cellulose Insulation

between studs

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Choice of Climatic Data

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Design Reference Year Actual 1981 - 2010 avg

Temperature

Max 24.4°C

Min -5.9°C

Mean 9.7°C

Temperature

Max 28.7°C

Min -4.7°C

Mean 9.8°C

Relative Humidity

Max 100%

Min 42%

Mean 84%

Relative Humidity

Mean 84%

Monthly means range from 76% - 87%

Rainfall

633mm/a

Rainfall

758mm/a

Results

Results: Normal Conditions-Point B

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Results: Normal Conditions-Point A

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Distribution of Data

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RH (%)

A. B.

C. D.

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Normal Conditions

Results: Additional Moisture Source

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• Moisture Source equivalent to 1% of the annual driving rain to simulate a failure in the building envelope is modeled in the outer 5mm of the timber stud.

• ASHRAE 160P

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Results: Additional Moisture Source

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Additional Moisture Source

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Normal Conditions

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Distribution of Data

A. B.

C. D.

Conclusion

• Initial results showed all wall types have similar Relative Humidity profiles, ranging from 75% to 85%.

• After the additional moisture source was introduced the profiles of each wall changed.

• Walls A and C show increasing Relative Humidity profiles consistently above the 80% threshold for mould growth.

• Walls B and D show decreasing Relative Humidity profiles seldom above 80%.

• The walls with the lowest RH values had the OSB located on the internal side of the stud.

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