Vapour barrier This is a layer of building material (e.g. a vapour barrier) designed to prevent water vapour from escaping from inside the building into the building structure (walls, ceilings). It protects against moisture condensation inside building partitions, which can lead to serious problems. These can include, amongst other things, material degradation, corrosion, a reduction in thermal insulation performance, and the growth of mould and fungi.
The vapour barrier is placed on the 'warm' side of the envelope, on the inside of the building. In this way, water vapour that naturally seeks to penetrate to the outside of the building is prevented from penetrating into the building envelope.
Vapour barrier in a timber-frame house
In timber-frame construction, it is important to ensure that continuity of the vapour barrier layer. This applies in particular to the junctions between walls and ceilings and roofs, to corners, and to points where cables or other service elements pass through a partition.
Simply using the right material does not guarantee that the vapour barrier will function correctly. The way in which joints are made and areas where its continuity might be compromised are also important.
