A Hygrothermal Analysis of International Timber Frame Wall
Assemblies:
Tested Under Temperate Maritime Climatic Conditions
Lee Corcoran
Dublin School of Architecture
Dr. Aidan Duffy Sima Rouholamin
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24.06.2013
Introduction
• Conference Paper.
• Central European Symposium on Building Physics.
• Paper Accepted 22-04-2013.
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Introduction
• Increase in timber frame construction since 1990.
photo: trada
photo: www.monreagh.com
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Problem Definition
• 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: Darren Bergin
photo: Darren Bergin
photo: www.findingmoldexperts.com
photo: www.dspinspections.com
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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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The Conventional Timber Frame
• Accounts for 90% of all Timber
structures in Ireland.
• Relies on membranes to protect
the structure from moisture.
• Highly vapour resistive racking
board commonly located on the
outer side of the the stud.
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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
over a selected period of time.
• Assess the drying capacity of each wall assembly by
modelling an additional moisture source.
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Literature Review
• Review of common timber frame construction methods.
• Review of testing methods.
– Laboratory tests
– Field tests
– Simulation using computer software
• Review of the simulation tools available.
– Overview of hygrothermal simulation tools
– WUFI
– Delphin
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Methodology Overview
• 4 wall assemblies were chosen for simulation based
on a review of common details.
• WUFI was used to carry out the hygrothermal
simulations. • Delphin was used as a means of verifying the WUFI
hygrothermal model.
• Climatic data: Dublin, Ireland.
• Time step: hourly over a 3 year period. • Additional moisture source modeled.
Wall Assemblies
Wall Type A
Wall Type B
Wall Type D
Choice of Climatic Data
• Temperate maritime climatic conditions. –Does not experience extreme temperature differences.
–Ireland & UK. –Parts of France, Norway, Denmark, Germany, Belgium.
• Climatic data derived from Meteonorm for Dublin
airport. • A Design Reference Year was used, giving hourly values
representing the most severe conditions that are likely to
occur once every ten years.
• EN 15026: 2007.
Simulation Set Up
• Geometry
• Grid
• Materials
• Initial conditions
• Boundary conditions
• Sources
• Computational parameters
• Critical locations
Results
• 2 critical points were analysed. • As mould and fungal decay is heavily dependent on
the presence of moisture, Relative Humidity levels at
these critical points was monitored. • The simulations were run under normal conditions
initially. • The simulations were then run again under the stress
of an additional moisture load.
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Results: Normal Conditions-Point A
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Results: Additional Moisture Source
• 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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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 indicating that their is insufficient drying
capacity in the assembly.
• Walls B and D show decreasing Relative Humidity
profiles seldom rising above the threshold of 80%.
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Conclusion
• The walls with the greatest drying potential had the
OSB located on the internal side of the stud. • The drying potential of the wall increases as the wall
is more vapour permeable to the external boundary.
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