Wall Cavities Are Now Mandatory in Zones 6, 7 and 8. Here's What That Actually Means.

One of the most significant changes in NCC 2025 isn’t getting nearly enough attention.

From 1 May 2026, buildings in climate zones 6, 7 and 8 now generally need a continuous drained and ventilated cavity behind external wall cladding. Direct-fix cladding, where cladding goes straight onto the frame or sarking with no gap behind it, is generally no longer permitted in these zones.

If you’re a builder, designer or certifier working in Victoria  or Western Australia right now, this change applies to you. NSW and TAS follow in May 2027.

And yet, in conversations across the industry, a lot of people are still finding out about it.

Why the change is happening

Australian homes have become significantly more airtight and better insulated over the past decade. That’s been good for energy efficiency. It’s been less straightforward for moisture management.

When a building is well sealed but poorly ventilated, moisture has nowhere to go. It sits inside wall cavities, against timber framing and behind cladding. Over time, that leads to condensation, mould, and the kind of structural decay that doesn’t show up until it’s expensive to fix.

Direct-fix cladding was part of that problem. With no cavity behind the cladding, any moisture that got past the external skin had nowhere to drain and no airflow to help it clear.

NCC 2025 addresses that directly. The mandatory wall cavity requirement gives moisture a clear path out of the wall, keeping the structure dry and the building performing the way it should over the long term.

This isn’t a new idea

Here’s what might surprise you. VENT Systems has been solving exactly this problem in New Zealand for over 15 years.

New Zealand’s construction industry learned this lesson the hard way through the leaky homes crisis of the late 1990s and 2000s, when thousands of homes built with direct-fix cladding suffered severe moisture damage. The response was a fundamental shift in how New Zealand builds walls, with drained and ventilated cavities becoming standard practice long before any code required them.

VENT has been supplying the products that create those cavities ever since. The VB20 ventilated batten has been doing this job in New Zealand walls for well over a decade, creating the continuous drainage and airflow path that keeps moisture moving and timber dry.

Australian codes have caught up to what the New Zealand industry established years ago. The products that have been doing this job reliably over there are available here, tested, and compliant.