The majority of residential buildings in New Zealand are of light timber frame construction incorporating a flexible wall underlay on the outer face of the external wall framing, directly behind the cladding.

Flexible wall underlay, when well installed, generally does what it is meant to do – that is providing an extra line of defence against water that may penetrate the cladding and therefore protecting the vulnerable wall framing while also restraining the insulation within the framing cavity.

However, rigid wall underlays, commonly known as rigid air barriers, do a far better job when used in place of flexible wall underlays.

They are more robust than flexible underlays hence they provide a very effective line of defence against water penetration through the cladding – they are also easier to install, more durable once installed, allowing them to act as a temporary cladding prior to the installation of the actual exterior cladding (which allows interior work to continue prior to final enclosure), while also providing a solid substrate for the installation of flashing tape to window and door openings and exterior penetrations.

They can also have the added benefit of providing bracing, fire and acoustic performance.

More buildings are using rigid air barriers due to the additional performance options and this will become the way we build in the future.