Thermal Bridging - NCC 2022
The Australian Building Codes Board (ABCB) has changed the requirements for thermal bridging in the 2022 National Construction Code (NCC).
All compliance pathways thermal bridging requirements, now prescribe that thermally bridged metal framed dwellings achieve a similar performance to thermally bridged timber framed dwellings. To offset any negative impacts of thermal bridging on steel framed dwellings, NatHERS allows for any other elements of the homes’ design to be improved.
Thermal bridging implementation
The current thermal bridging implementation methodology can be found in CSIRO’s Thermal Bridging Implementation in AccuRate Report (2023). This report also includes a comparison of energy rating results between the previous method and the current method.
In 2020 in preparation for the thermal bridging updates to the NCC, a Thermal Bridging Report was published by CSIRO. This report included a set of thermal bridging default parameters and draft modelling guidance, as well as the impact of applying defaults on residential building energy ratings.
NatHERS thermal bridging function
NatHERS has been modified to include a thermal bridging function, based on CSIRO's Thermal Bridging Implementation in AccuRate Report (2023) and Thermal Bridging Report (2020) with the following features:
- Thermal bridging will not apply to timber framed constructions, ratings of timber framed dwellings will be unaffected.
- Thermal bridging calculations will only apply to repeating steel frame elements (e.g. joists and studs) for floors, walls and ceilings. Default values will be used when the precise framing specifications are not provided at the time of rating.
- The performance of thermally bridged metal framed dwellings will achieve a similar performance to thermally bridged timber framed dwellings i.e. will not reflect their performance in reality but will align with the performance of its timber counterpart.
- Thermal bridging impacts will be based on the calculation method outlined in standard NZS 4214:2006 Methods of determining the total thermal resistance of parts of buildings.