Warmer drier healthier #6: Thermal bridging in external timber-framed walls (part 2)

Abbreviation
BRANZ Research Now - Warmer drier healthier #6
Valid from
1/08/2021

Information provider
BRANZ Limited
Information type
Research report
Format
PDF

Description

The first part of the Thermal bridging in external timber-framed walls project found that the percentage of timber framing in the walls of new houses was much higher than generally assumed. This suggests that designed R-values are not being achieved in practice.

Part 2 of the project, outlined in this Research Now, focused on the causes, impacts and potential solutions to the problem.

The result of this research:

  1. This research found that standard 90 mm timber-frame construction complying with the Building Code produces new-build houses with actual whole-wall construction R-values that vary between R1.2–R1.4, even with R2.8 insulation installed. This highlights a sizeable performance gap between what is achieved in reality and the R-values calculated to meet Building Code compliance of R1.9/R2.0 in NZS 4218:2009.
  2. The research found little unnecessary timber in wall framing – each piece is added for valid regulatory and practical reasons. Even one of New Zealand’s most experienced frame and truss detailers working on a simple design could not reduce the framing percentage below 25%. Optimising the framing percentage alone will not achieve actual entire wall R-values that match those of minimum construction R-values for wall areas in NZS 4218:2009. A number of homes already built or currently under construction have overcome the problem of thermal bridging by using a second layer of insulation. This creates a thermal break between the timber framing and the external environment as well as providing space to increase the thickness of the insulation.

Scope

This Research Now includes:

  • Part 2 of the project
  • Exploring drivers for higher framing percentages
  • The impacts of high framing content and weak points
  • Advanced framing and insulation solutions
  • Two layers of insulation offer a range of benefits
  • Conclusion

 

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Warmer drier healthier #6: Thermal bridging in external timber-framed walls (part 2)

This document is not CITED BY any other resources:

Warmer drier healthier #6: Thermal bridging in external timber-framed walls (part 2)

Description

The first part of the Thermal bridging in external timber-framed walls project found that the percentage of timber framing in the walls of new houses was much higher than generally assumed. This suggests that designed R-values are not being achieved in practice.

Part 2 of the project, outlined in this Research Now, focused on the causes, impacts and potential solutions to the problem.

The result of this research:

  1. This research found that standard 90 mm timber-frame construction complying with the Building Code produces new-build houses with actual whole-wall construction R-values that vary between R1.2–R1.4, even with R2.8 insulation installed. This highlights a sizeable performance gap between what is achieved in reality and the R-values calculated to meet Building Code compliance of R1.9/R2.0 in NZS 4218:2009.
  2. The research found little unnecessary timber in wall framing – each piece is added for valid regulatory and practical reasons. Even one of New Zealand’s most experienced frame and truss detailers working on a simple design could not reduce the framing percentage below 25%. Optimising the framing percentage alone will not achieve actual entire wall R-values that match those of minimum construction R-values for wall areas in NZS 4218:2009. A number of homes already built or currently under construction have overcome the problem of thermal bridging by using a second layer of insulation. This creates a thermal break between the timber framing and the external environment as well as providing space to increase the thickness of the insulation.

View on Information Provider website Download this resource (PDF, 834KB)
Warmer drier healthier #6: Thermal bridging in external timber-framed walls (part 2)
Description

The first part of the Thermal bridging in external timber-framed walls project found that the percentage of timber framing in the walls of new houses was much higher than generally assumed. This suggests that designed R-values are not being achieved in practice.

Part 2 of the project, outlined in this Research Now, focused on the causes, impacts and potential solutions to the problem.

The result of this research:

  1. This research found that standard 90 mm timber-frame construction complying with the Building Code produces new-build houses with actual whole-wall construction R-values that vary between R1.2–R1.4, even with R2.8 insulation installed. This highlights a sizeable performance gap between what is achieved in reality and the R-values calculated to meet Building Code compliance of R1.9/R2.0 in NZS 4218:2009.
  2. The research found little unnecessary timber in wall framing – each piece is added for valid regulatory and practical reasons. Even one of New Zealand’s most experienced frame and truss detailers working on a simple design could not reduce the framing percentage below 25%. Optimising the framing percentage alone will not achieve actual entire wall R-values that match those of minimum construction R-values for wall areas in NZS 4218:2009. A number of homes already built or currently under construction have overcome the problem of thermal bridging by using a second layer of insulation. This creates a thermal break between the timber framing and the external environment as well as providing space to increase the thickness of the insulation.
View on Information Provider website Download this resource (PDF, 834KB)
This resource does not cite any other resources.

Warmer drier healthier #6: Thermal bridging in external timber-framed walls (part 2)

This resource does not CITE any other resources.
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