Lee Corcoran Dublin School of Architecture Dr. Aidan Duffy Sima - - PowerPoint PPT Presentation

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

• Percentage of housing units completed using timber frame

construction in Ireland.

Introduction

2 Source: ITFMA, 2004

to put this in context...

3 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
• n the presence of moisture or high Relative Humidity.
• Moisture related problems include:

–Mould growth –Fungal decay

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

4

5 photo: www.dspinspections.com photo: Darren Bergin photo: Darren Bergin photo: www.findingmoldexperts.com

Problem definition

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

6

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.

7

Typical Timber Frame

8

• 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.

9

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.

10

Wall Assemblies

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

*Wall Type C uses Cellulose Insulation between studs

11

Choice of Climatic Data

12

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

14

Results: Normal Conditions-Point A

15

Distribution of Data

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

A. B. C. D.

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

Normal Conditions

Results: Additional Moisture Source

17

• Moisture Source equivalent

to 1% of the annual driving rain to simulate a failure in the building envelope is modeled in the outer 5mm

• f the timber stud.
• ASHRAE 160P

18

Results: Additional Moisture Source

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

Additional Moisture Source

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

Normal Conditions

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 70 75 80 85 90 95 More

Time (hours) RH (%)

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
• n the internal side of the stud.

20