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
09.09.2013
Thursday 10 October 13
Introduction
• Percentage of housing units completed using timber frame
construction in Ireland.
Source: ITFMA, 2004
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to put this in context...
50%+ by 2011
Source: ITFMA, 2003
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Thursday 10 October 13
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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Thursday 10 October 13
photo: Darren Bergin
photo: Darren Bergin
photo: www.findingmoldexperts.com
photo: www.dspinspections.com
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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
• Plasterboard with internal finish
• Vapour control layer
• Vertical/Horizontal timber
members
• Insulation
• Sheathing board
• Breather membrane
• Ventilated cavity
• External cladding
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Thursday 10 October 13
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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Thursday 10 October 13
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 Assemblies
Wall Types A+C*
Wall Type B
Wall Type D
*Wall Type C uses Cellulose Insulation
between studs
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Climate
• Ireland and the UK
• Predominant climate across western Europe
• New Zealand and southeast Australia
• Coastal northwestern North America
• Portions of southwestern South America
• Small areas of Africa
Map Source: Wikipedia
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Choice of Climatic Data
Actual 1981 - 2010 avg
Design Reference Year
Temperature
Relative Humidity
Temperature
Relative Humidity
Max
24.4°C
Max
100%
Max
28.7°C
Mean 84%
Min
-5.9°C
Min
42%
Min
-4.7°C
Monthly means range
from 76% - 87%
Mean 9.7°C
Mean 9.8°C
Mean 84%
Rainfall
Rainfall
633mm/a
758mm/a
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Results
Thursday 10 October 13
Results: Normal Conditions-Point B
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Results: Normal Conditions-Point A
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Distribution of Data
20000
B.
18000
16000
18000
16000
Time (hours)
Time (hours)
A.
20000
14000
12000
10000
8000
6000
4000
14000
12000
10000
8000
6000
4000
2000
2000
0
0
70
75
80
85
90
95
More
70
75
80
RH (%)
C.
D.
20000
18000
95
More
90
95
More
20000
18000
16000
Time (hours)
14000
12000
10000
8000
6000
14000
12000
10000
8000
6000
4000
4000
2000
2000
0
0
70
75
80
85
RH (%)
90
95
More
70
75
80
85
RH (%)
Normal Conditions
Thursday 10 October 13
90
RH (%)
16000
Time (hours)
85
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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Thursday 10 October 13
Results: Additional Moisture Source
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Thursday 10 October 13
Distribution of Data
20000
B.
18000
16000
18000
16000
Time (hours)
Time (hours)
A.
20000
14000
12000
10000
8000
6000
4000
14000
12000
10000
8000
6000
4000
2000
2000
0
0
70
75
80
85
90
95
More
70
75
80
RH (%)
C.
D.
20000
18000
95
More
90
95
More
20000
18000
16000
Time (hours)
14000
12000
10000
8000
6000
14000
12000
10000
8000
6000
4000
4000
2000
2000
0
0
70
75
80
85
RH (%)
90
95
More
70
75
80
85
RH (%)
Normal Conditions
Additional Moisture Source
Thursday 10 October 13
90
RH (%)
16000
Time (hours)
85
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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Thursday 10 October 13