AVCL jointing requirements
100 mm
Joints in air and vapour control membranes must be adequately lapped, typically with a minimum overlap of 100mm, to ensure continuity of the membrane
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Read the full answerJoints in air and vapour control membranes must be adequately lapped, typically with a minimum overlap of 100mm, to ensure continuity of the membrane. These joints should ideally be supported by underlying structural elements like studs or noggings.
Basis in regulation
How to check it on site
Check that all AVCL joints have the specified minimum lap and are properly supported where possible.
Common failure
Inadequate lapping or unsupported joints can create weak points in the AVCL, leading to air leakage and vapour ingress.
Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.