Air tightness membranes help in preventing unwanted air infiltration and loss of heat. Their main task is to protect timber structures in a building, for example, the roof structure, against condensation, normally caused by humid and warm room air during winter. Its function has made most building professionals call it to vapour control layers. Airtight membranes help make buildings airtight, ensuring high comfort and health and minimum heating requirements. Without proper airtightness membranes, insulation has little ability to keep the building warm. Therefore, it must be at the forefront of the design.

When placing the membranes, the builders first ensure that the surface is dry and clean to receive an airtightness membrane tape. That caveat implies that when the surface is friable or loose, it must be stabilized using a system primer. The system primer ensures the surface is bound together, but also, there is stickiness which will hold the tape. All masonry surfaces, historic surfaces and weathered wood fibre boards should be primed before applying the airtight membrane tape. Tapes with split backings are necessary but quite expensive. With a lot of care and a sharp new blade on a craft knife, you can score down the back of a standard tape.