The question every steel-frame builder eventually googles
How thick does a thermal break need to be? How thick is a thermal break strip? Is 10 mm of tape enough? They're fair questions – and they're some of the most-searched thermal break questions in Australia right now. The catch is that the National Construction Code never answers them in millimetres. Nobody should have to reverse-engineer the Code on the back of a ute to work that out, so here it is in plain terms.
What the NCC actually asks for
The requirement is performance, not thickness. For steel-framed walls with lightweight cladding, the NCC requires a thermal break with a minimum R-value of R0.2 between the cladding and the frame, installed at all points where the cladding would otherwise contact the steel (NCC Housing Provisions Part 13.2.5). Studs and plates, noggins and horizontal battens – all of them. Nothing in the provision says "so many millimetres thick", because R-value measures resistance to heat flow, and that depends on the material every bit as much as the depth of it.
A couple of state variations are worth knowing: the Northern Territory and Tasmania have no steel-frame thermal-break requirement, and New South Wales frames it as "to the degree necessary" (H6P1). Everywhere else, R0.2 is the floor. As always, confirm the requirements that apply where you build.
Why thickness alone can't answer it
Two products at the same thickness can land either side of the line. Shop the market and you'll see why the question needs reframing. There are tapes advertising R0.2 at around 10 mm – on the minimum with nothing in reserve. There are reflective foil products claiming thermal-break performance that are actually Class 1 or 2 vapour barrier membranes: limited to Climate Zones 1–3 and typically needing a 20 mm still-air gap in front of them to deliver the claimed R-value at all. In Climate Zones 4–8 – exactly where the thermal break matters most – those foils are out of their depth.
And the air gap itself? A sealed 20 mm still-air space is only worth around R0.15–0.17 – already under the minimum – and once the cavity is ventilated, standard calculation methods strip its value back to roughly R0.04. Air is not a thermal break, and millimetres of the wrong material aren't either.
The one place a millimetre number does apply
Don't confuse the thermal break with the condensation cavity. These are two separate NCC obligations that the market constantly blurs. The energy provision wants a thermal break of at least R0.2 – a performance value. The condensation provision (Housing Provisions Part 10.8) wants, where triggered, a drained and ventilated cavity at least 12 mm deep in Climate Zones 6, 7 and 8 – and that one genuinely is a depth, with no R-value attached to it. Meeting one does not meet the other. A wall in a cold climate zone generally has to answer both.
So how do you choose?
Pick by R-value first and let thickness follow. ATI's Cavi-Break® and Cavi-Vent® strips make the numbers easy: X10 delivers an indicative material R-value of R0.28, X12 delivers R0.32, X20 delivers R0.58 and X35 delivers R0.90 (indicative material values, not whole-wall R-values). Every variant clears the R0.2 minimum with margin, rather than scraping it. The 12 mm X12 earns its keep twice in Climate Zones 6–8: R0.32 of material R-value on the energy side, and the 12 mm cavity depth the condensation provision asks for when it's used as a cavity batten in a drained and ventilated application. Cavi-Vent® adds integrated drainage and ventilation pathways, and the self-adhesive strips peel and stick over every member – studs, plates, noggins – so the break is continuous, not partial.
Easier, better, healthier
Get the R-value right and the wall gets better – it performs closer to the number you specified instead of quietly leaking heat through the frame. The install gets easier – peel-and-stick beats packing and fixing. And the home gets healthier – a warmer frame gives moisture fewer cold surfaces to settle on, though remember the NCC's own explanatory notes: condensation management measures may not prevent condensation from occurring. That's exactly why margin beats minimum.
Your next step
Stop guessing in millimetres. Use ATI's free Total Wall R-Value Comparison tool to model your wall and see what each thermal break option really does to the numbers – then request a sample and put it on one job. Tell us your wall system and climate zone and we'll point you to the right variant and the data behind it, through our technical support and approved reseller channels.
australianthermal.com.au
Australian Thermal Industries makes Cavi-Break® and Cavi-Vent® – thermal break and cavity ventilation systems for Australian residential and light commercial construction. 10-year warranty. 100% recyclable. Independently tested. General guidance only, not a compliance determination – confirm the requirements for your project, climate zone and jurisdiction against the NCC.
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