Wall Cavities: What Builders Need to Know

Dry and Ventilated Wall Cavities

With NCC 2025 requirements bringing greater focus to wall cavities, getting it right is increasingly important for builders. At Bowens Building and Innovation Expo 2026, attendees had the opportunity to hear from Devin Grant, Director at Performance Membranes. He discussed the need to provide ventilation and drainage while also protecting the home from insects and vermin. This is what we learnt.

Why Do We Need a Drained and Ventilated Cavity?

“Drainage and ventilated, those are two really key words,” Devin said.

Why? Because the cavity needs to do two jobs: drain and ventilate. Without adequate drying and drainage behind the cladding, moisture build up can cause condensation, mould and eventually timber rot.

A ventilated and drained cavity provides a pathway for airflow and moisture to escape behind external cladding. The external wall systems in climate zones 6, 7 and 8 require a minimum 12 mm clear cavity formed using cavity battens, spacers or an equivalent solution as per NCC requirements.

The Importance of Keeping the Cavity Clear

Meeting the minimum cavity width is one thing; maintaining a clear cavity on site is another. Insulation can push into the cavity and obstruct airflow, not to mention debris and building materials that can fall into the wall cavity during construction.

That’s why ensuring the cavity is clear prior to installing top and bottom cavity closers is so important.

Performance Membranes Cavity Closers Solutions

Performance Membranes offers cavity closers designed for base-of-wall and wall-top applications. The range includes 70mm, 55mm, 35mm, 20mm and 12mm options, with 2 mm apertures designed to provide ventilation while helping protect against vermin and insects.

“Making it vermin proof is a big component,” Devin said.

Benefits of Cavity Closers;

• Maintains airflow behind the cladding
• Stops insects, vermin, and debris from entering the cavity
• Suitable for common cladding systems
• Available in a range of sizes
• Designed to meet ember protection requirements in accordance with AS 3959:2018 (BAL Low to BAL 40) when used as part of a compliant assembly
• Supports condensation management strategies under NCC 2022 when incorporated into a correctly detailed wall system
• Provides a consistent method for integrating ventilation and drainage.

For more information about this product, explore cavity closer products online or drop into a Bowens store for expert advice. You can also learn more about ventilation, airtightness and moisture management solutions at the Rethink Building Hub in Hastings.

Explore the virtual Rethink Building Hub to see what’s on offer. For questions or bookings, contact our Rethink Building team.