Vapour barrier film is a thin layer of material, usually plastic (e.g. PE or aluminium), used in the building envelope to stop water vapour from penetrating into the thermal insulation layers. It is usually installed on the inside of a wall or roof, i.e. on the room side. Its purpose is to protect against condensation inside the structure, which could lead to dampness, fungal growth or a decrease in insulation properties.
In modern buildings, the vapour barrier is an indispensable part of the roof and frame walls. It is important that it is laid tightly - joints should be sealed with special tape and penetrations through installations carefully sealed.
