A Problem of Our Own Making

The push for higher energy efficiency has transformed how Australian homes are built. Tighter envelopes, better insulation, and improved vapour control have delivered real performance gains — but they’ve also created a new problem: buildings that can’t breathe. 

In Climate Zones 6, 7, and 8, where temperature differentials are greatest, moisture-laden interior air condenses inside wall cavities and roof spaces with nowhere to go. The result, in buildings without adequate ventilation, is structural degradation, mould growth, and compromised indoor air quality — outcomes that erode the very performance gains the design set out to achieve. 

NCC 2025 is the industry’s formal acknowledgement of this problem, and its remedy. 

What’s Changing Under NCC 2025?

The core change is the end of direct-fix cladding in Climate Zones 6, 7 and 8. From 1 May 2026, new construction in these zones must incorporate a drained and ventilated cavity behind external cladding — a system designed to allow moisture to escape and air to circulate continuously within the wall assembly.

Roof ventilation requirements are also extended, now applying to Zones 4 and 5 in addition to the existing cooler zones. And vapour permeable membranes become mandatory on the exterior side of primary insulation across all climate zones.

For architects and designers, this means cavity construction details need to be embedded in specifications from the outset — not retrofitted at construction stage. The compliance deadline is approaching quickly, and many states are able to adopt the new code with little to no lead time.

Image: ©Australian Building Codes Board, licensed under CC-BY 4.0.

More Than a Compliance Response

Well-specified cavity systems deliver benefits that go well beyond ticking a code box. A continuous air gap behind cladding improves the thermal performance of the wall assembly, reduces long-term maintenance risk, and creates the conditions for genuinely healthier buildings — outcomes that matter to the clients architects and designers serve.

For architects and designers, specifying a high-performance cavity system is one of the clearest ways to protect a building’s long-term integrity — and to demonstrate that energy efficiency and occupant health are not competing priorities.

Photo: Vertical cladding systems like this demand a wall assembly built to perform behind the facade. NCC 2025 makes that a code requirement. 

Mould and mildew don’t just look bad — they pose serious risks to both the structure and the people inside. Trapped moisture can degrade building materials over time and even contribute to airborne pollutants, which is why ensuring continuous ventilation behind cladding is so important.

Nick Higgins, Founder, Highwood Timber

Specifying with Confidence: Highwood’s HighFlow System

Highwood Timber developed the HighFlow Cavity Batten specifically to address the condensation management challenge — and the product is designed to exceed NCC 2025 requirements, not simply meet them.

Made from engineered LVL timber and H3 treated for durability, the HighFlow Batten creates a 36mm ventilated cavity behind cladding, with grooved channels that deliver approximately 2,000mm² of ventilation per linear metre. A chamfered top edge ensures drainage away from the frame. Because it is a structural element, it spans between studs without additional nogging — simplifying the construction detail and reducing on-site labour.

The system is compatible with fibre cement, vertical timber, and sheet claddings, giving specifiers flexibility without sacrificing performance. Highwood also offers the HighLine Batten — a vertical cavity batten for off-stud applications — for projects where horizontal battening isn’t the preferred approach.

Image: The HighFlow Cavity Batten — engineered grooves, chamfered drainage edge, and LVL construction that stays straight on site and in service.

We designed the HighFlow Cavity Batten to solve a real problem in the industry — builders were struggling to balance moisture control with structural integrity. By improving airflow and drainage behind the cladding, we’re helping create healthier, longer-lasting buildings that comply with the latest regulations.

Nick Higgins, Founder, Highwood Timber

Act Now, Specify with Confidence

NCC 2025 adoption is imminent. For architects and designers working on projects in the affected climate zones, the time to embed compliant cavity details into documentation is now — before the deadline removes the option of a staged transition.

Highwood Timber’s HighFlow system offers a straightforward, well-engineered path to compliance — one that supports better building outcomes rather than simply satisfying a regulatory requirement. Contact the Highwood team to discuss specification details for your next project.

Image: Highwood Cavity Batten provide cleaner airflow, better moisture control and a healthier wall system overall.

Want to learn more about how Highwood Timber's cavity batten system can work for your next project?

Connect with Yasmin Munro to find out more.

Frequently Asked Questions

When do the NCC 2025 ventilation requirements take effect?
Most states can adopt the new code from 1 May 2026, with little to no guaranteed grace period. The ACT has a confirmed deadline of 1 November 2026. Architects and designers working on projects in affected climate zones should be embedding compliant cavity details into documentation now.

Which climate zones are affected by the mandatory ventilated cavity requirement?
The direct-fix cladding ban and mandatory drained and ventilated wall cavity requirement applies to Climate Zones 6, 7 and 8 — covering much of southern and alpine Australia. Expanded roof ventilation requirements also now extend into Zones 4 and 5. 

Does this affect all cladding types? 
Yes. Any lightweight external cladding in the affected climate zones will need to be fixed over a compliant ventilated cavity system rather than direct to the frame or sarking. This applies regardless of whether the cladding is fibre cement, timber, or sheet-based.

How does the HighFlow Cavity Batten simplify NCC 2025 compliance for my projects?
The HighFlow Batten is designed as a structural element, meaning it spans between studs without additional nogging or cross-battening. It creates a 36mm drained and ventilated cavity that exceeds NCC 2025 minimums, and is compatible with a broad range of cladding systems — reducing the need for project-specific workarounds at the documentation stage.

Is a ventilated cavity just a compliance requirement, or does it add genuine value to a building?
Both. Beyond satisfying the code, a well-specified cavity system improves the thermal performance of the wall assembly, reduces long-term maintenance risk, and supports healthier indoor environments by preventing mould and moisture accumulation. For clients focused on building longevity and occupant wellbeing, it's a meaningful specification decision — not just a regulatory response.

Where can I get specification details for the Highwood cavity batten system?
The Highwood team can provide full specification documentation, product details, and technical support for your project. Visit highwood.com.au or contact them directly to discuss your requirements.