In the pursuit of energy-efficient homes, thermal bridging often remains a hidden yet powerful culprit that undermines building performance. Despite sophisticated insulation strategies, air-sealing measures, and advanced modelling, these tiny shortcuts for heat flow can silently erode the effectiveness of thermal envelopes — increasing energy use and reducing comfort.
For NatHERS assessors, failure to address and properly model thermal bridging can result in inaccurate star ratings, non-compliance with the National Construction Code (NCC), and buildings that ultimately fail to perform as designed.
Table of Contents
What Is Thermal Bridging?
Thermal bridging occurs when conductive materials form a pathway across insulation layers, allowing heat to bypass thermal barriers and flow in or out of the building more easily. This is especially problematic in modern lightweight construction, where structural elements such as steel or concrete frequently interrupt insulation layers.
While the concept sounds subtle, the impact is substantial. Research shows that thermal bridging can reduce heating loads by roughly 25 to 30% depending on the climate zone(ABCB, 2022).
Common Examples of Thermal Bridges in Residential Buildings
Thermal bridges occur more often than many designers or assessors realise. Below are typical locations where they are often found:
1. Steel Framing in External Walls
Steel has a high thermal conductivity compared to timber and insulation materials. In steel-framed buildings, studs, plates and lintels create repeating linear thermal bridges throughout external walls.
If thermal breaks are not installed, heat can easily bypass insulation batts, which significantly decreases the R-values of the walls. The NCC 2022 now mandates modelling these effects in NatHERS simulations (NatHERS Technical Note, 2023).
2. Floor Slab Edges and Balcony Connections
Where internal floor slabs or balconies penetrate the building envelope (often in apartments or split-level homes), they act as direct heat paths. Without slab edge insulation or thermal breaks, winter heat is rapidly lost through exposed concrete elements.
3. Roof-to-Wall Junctions
Where pitched roofs meet external walls, insulation is often compressed or missing entirely to accommodate roof battens and eaves construction. This leaves gaps that act as cold bridges, especially in climates with significant winter heating loads.
4. Window and Door Frames
Metal window frames (particularly aluminium without thermal breaks) are notorious for creating point thermal bridges. Even where double glazing is used, conductive frames can allow heat to bypass insulated walls.
5. Junctions Between Walls and Intermediate Floors
In multi-storey homes, intermediate floor joists often interrupt wall insulation at floor levels, allowing heat to transfer vertically between conditioned and unconditioned spaces.
6. Service Penetrations and Fixings
Areas where plumbing pipes, electrical conduits, or structural fixings (e.g. steel angles and bolts) penetrate the thermal envelope are often uninsulated, creating small but numerous point thermal bridges.
Thermal Bridging and NatHERS Star Ratings
The impact of these thermal bridges is more than theoretical. In NatHERS software (FirstRate5, HERO, AccuRate), poor detailing and lack of modelling for thermal bridging can artificially inflate performance ratings — or, when correctly modelled, reveal that designs fall short of 6-7 star minimum targets.
The NCC 2022 introduced significant reforms to energy performance expectations in housing. Clause J1.6 of NCC Volume Two, 2022 states that for steel-framed external walls, the effects of thermal bridging must be included in the total R-Value calculation unless thermal breaks of R0.2 or greater are installed.
To support consistency, NatHERS published the Thermal Bridging Guidance Note (2023) requiring assessors to model default or actual thermal bridging effects when applicable.
Failing to do so risks AAO audit issues, star rating downgrades, and buildings that simply won’t perform in practice.
Mitigating Thermal Bridges: Design and Construction Solutions
Mitigating thermal bridging requires careful design detailing and material selection:
Thermal Breaks
The most common solution in steel framing and balcony connections is to insert thermal breaks — low conductivity materials placed between conductive elements and the external environment.
Materials such as rigid foam board, insulated battens or proprietary break products (rated R0.2 or higher as required by NCC) can be used.
Continuous Insulation
Continuous insulation (CI) systems effectively install insulation on the exterior of wall framing without gaps, significantly reducing the risk of thermal bridging at junctions. External insulation solutions such as insulated cladding systems can help.
Improved Detailing at Junctions
Architects and designers can detail better connections at floor-to-wall, wall-to-roof, and window junctions to allow space for insulation continuity and avoid compressing insulation in tight cavities.
Use of Thermally Improved Frames
Where possible, use window and door frames with thermal breaks — especially aluminium systems. This helps prevent linear bridges across openings.
Education and Supervision On-Site
Ultimately, even perfect designs can be undermined on-site. Poor installation of insulation and thermal breaks can leave gaps or bridges that reduce thermal performance. Supervising trades and educating installers is essential to ensure correct implementation.
Conclusion: Why It Matters More Than Ever
As Australia moves rapidly towards net-zero targets and more stringent residential energy standards, the performance gap between ‘designed’ and ‘as-built’ efficiency is increasingly under the microscope.
Thermal bridging is no longer something that can be ignored or left to chance. NCC 2022 has elevated its importance by embedding requirements for modelling and mitigation in mainstream construction regulation.
For NatHERS assessors, accurate and consistent modelling of thermal bridging — particularly in steel framed and complex residential designs — is now critical to delivering compliant and realistic energy ratings.
For architects and builders, better design detailing and material choices can eliminate many common bridges, improve occupant comfort, and achieve higher star ratings without expensive after-the-fact redesign.
Ultimately, thermal bridging is the hidden energy leak that — if left unchecked — can sabotage performance and compliance. But careful attention, good design, and rigorous assessment will eliminate these issues effectively.
Further Reading and Resources
- NCC 2022 Volume Two (See Section J1.6)