Thermal bridging
Thermal bridging is heat flowing through a more conductive building element, bypassing insulation. NCC 2022 H6D2 requires R0.2 thermal breaks on steel framing.
Ask Chalkline about this →Thermal bridging is the movement of heat through a building element that conducts more readily than the surrounding material, bypassing the insulation layer. The classic example: each steel stud or metal batten in a wall frame runs from the warm interior to the cold exterior, and heat travels along the steel rather than through the (more resistive) bulk insulation in the stud cavity.
Steel conducts heat approximately 400 times more readily than structural timber, so light-gauge steel framing creates a significantly stronger bridge effect than a timber-framed equivalent. Without thermal breaks at cladding-to-frame contact points, a steel-framed wall can lose 0.7 to 1.2 NatHERS stars against a comparable timber-framed wall (NatHERS Assessor Handbook, verified 2026-05-10).
Where thermal bridges appear on a residential build
Beyond steel studs, common bridge paths a builder will recognise on site:
| Element | Bridge mechanism |
|---|---|
| Steel stud, metal batten, top-hat batten | Frame-to-cladding contact, full wall height |
| Concrete slab edge (perimeter) | Slab thermal mass exposed to outside air |
| Steel lintel over openings | Conductive member spans the cavity |
| Cantilevered balcony slab | Conditioned floor extends to unconditioned outside |
| Fasteners through rigid insulation | Each screw is a localised bridge |
| Rim/header joists at floor band | Often left uninsulated |
| Window head + sill | Frame, lintel, jamb contact |
NCC 2022 thermal-break requirement (steel framing)
Under NCC 2022 Volume Two clause H6D2(2)(a)(v), where steel framing is used in external walls and the steel conductivity exceeds 50 W/(m·K), a thermal break of at least R0.2 must be installed between the steel frame and the external lightweight cladding (verified 2026-05-24, ABCB NCC Navigator: thermal bridging in residential buildings).
Acceptable thermal-break materials:
- Timber batten ≥20 mm thick
- Expanded polystyrene (EPS) strip ≥12 mm thick
- Continuous rigid foam sheet ≥R0.2
The rule kicks in specifically when the external cladding (weatherboards, fibre cement, metal sheet) is fixed directly to the metal frame OR when the internal lining is also fixed directly to the same member. A timber-batten cavity behind the cladding doubles as the thermal break in many residential builds.
Why it matters for the 7-star target
NCC 2022 requires Class 1 buildings to reach a NatHERS 7-star equivalent (Part H6). Unmanaged thermal bridging in a steel frame can be the difference between passing and failing the energy assessment. NatHERS assessors now model thermal bridges explicitly using updated 2022 derating coefficients per the NatHERS Thermal Bridging chapter (December 2023). Builders should request the assessor’s stud-derating treatment on steel-frame jobs to confirm star-rating compliance early.
Also known as: thermal bridge, thermal bridges.
Category: Energy efficiency, framing.
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Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.