Breather membrane
The purpose of the membrane is to allow water vapour to permeate through from the insulation into the cavity above and yet prevent water from the cavity entering the quilt.
Breather membranes are installed over the top of quilt insulation and below the external profiled sheet.
Breather membranes should not be considered in isolation as a means of preventing or limiting interstitial condensation, however. The inclusion of sealed liners or vapour control layers with vented filler blocks should be regarded as the first step. The membrane should be detailed to allow drainage down the slope of the roof and should be stretched across the spacers to prevent water from ponding.
Finally, all side and end laps of membranes should have an overlap of at least 150 mm.
