The R-value on paper isn’t the R-value in the wall
Here’s a frustration builders run into the moment they dig into the NCC: the batt says R2.5, the spec says R2.5, but the wall doesn’t perform at R2.5. The gap has a name – thermal bridging – and once you can see it, you can’t unsee it. Fair enough that it’s confusing: nobody should have to reverse-engineer the Code to work out why their insulation isn’t pulling its weight. So here it is in plain terms.
What thermal bridging actually is
Thermal bridging is heat taking a shortcut. Insulation batts sit between the frame members and slow heat down. But the frame members themselves – studs, top and bottom plates, noggins, battens – conduct heat far faster than the batts beside them. Heat flows along the path of least resistance, so it runs straight through the frame, bypassing the insulation. In winter it escapes through the frame; in summer it pours in. The batt is doing its job; the frame is undoing part of it.
Steel is the worst offender because it conducts heat roughly a thousand times better than timber. A steel-framed wall without a break can shed close to half of its nominal batt R-value – you can’t see it until a thermal camera, a certifier, or a condensation problem finds it.
Where it happens in a wall
Everywhere the frame touches the cold side. The obvious bridges are the vertical studs. The ones builders forget are the horizontal members – the top and bottom plates, the noggins, and any horizontal battens. Every one of those is a line of frame running from the warm inside to the cold outside. Heat flow is governed by the weakest link, not the average, so a single un-broken cold line drags the whole wall’s assessed performance down with it.
Can thermal bridging cause condensation? Yes – and that’s the bigger risk
This is the part that turns an energy problem into a moisture problem. A cold steel member running through the wall is the exact surface where warm, moist indoor air condenses on a cold night. Break the studs but leave the plates and noggins cold, and those horizontal lines become the prime spots for interstitial condensation – the hidden kind that shows up months later as damp, corrosion or mould when someone finally opens the wall. So the thermal break isn’t only about energy bills. It’s about keeping the frame warm enough that moisture doesn’t have a cold surface to settle on.
How the NCC deals with it
Australia’s National Construction Code tackles thermal bridging through its energy efficiency provisions. For steel-framed walls with lightweight cladding, a thermal break of at least R0.2 is required between the external cladding and the steel frame, installed at all points where the cladding would have come into contact with the frame (NCC Housing Provisions Part 13.2.5). “All points” is the key phrase – studs and plates, noggins and horizontal battens, not just the easy vertical runs.
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, the R0.2 minimum applies. As always, confirm the requirements and the commencement date that apply where you build.
How to break the bridge
Put a continuous thermal break between the cladding and the frame – over every member. This is where ATI’s Cavi-Break® and Cavi-Vent® strips earn their place. The flagship 20 mm strip carries an indicative material R-value of R0.58 – around three times the R0.2 minimum the NCC asks for (that’s an indicative material value, not a whole-wall R-value). Because it sheaths the steel-to-cladding interface, it lifts the temperature of the frame so there are fewer cold surfaces for heat to escape through or moisture to condense on. Cavi-Vent® adds integrated ventilation channels so the same strip also helps the wall drain and breathe, and the self-adhesive strip peels and sticks in seconds – no tools, no fixings.
The one rule that matters: break every interface, not just the studs. A partial break leaves an open steel path, and the physics doesn’t care that you got most of it.
The easier, better, healthier build
Get the thermal break right and the wall gets better – it actually performs at the R-value you specified, instead of quietly leaking it away. The build gets easier, because a peel-and-stick strip is faster than screw-fixing timber. And the home ends up healthier – a warmer frame with fewer cold surfaces is a wall that keeps damp and mould out long after handover. That’s the quiet win of closing the gap between the R-value on paper and the R-value in the wall.
Your next step
Want to see what thermal bridging is really costing your wall? Use ATI’s free Total Wall R-Value Comparison tool to model your assembly and see how a higher-R thermal break changes the numbers. Then request a sample, try it on one project, and decide for yourself. Tell us your wall system and climate zone and we’ll point you to the right product and the data to back 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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