Vapour barrier is any damp-proofing material, usually a plastic or foil sheet, that prevents the diffusion of moisture through building walls, floors, ceilings, or roof assemblies to avoid packing and interstitial condensation. Since they have different levels of permeability, several of these materials are technically simply vapor retarders.
Vapor diffusion retarders are normally available as coatings or membranes. The membranes are technically flexible and thin materials, but sometimes include thicker sheet materials named "structural" vapor diffusion retarders. The vapor diffusion retarders vary from all kinds of materials and keep updating every day, some of them nowadays even combined the functions of other building materials.
In regions where heating predominates, an interior vapor retarder is useful, whereas an outside vapor retarder is useful in situations where cooling predominates. In most regions, it is frequently preferable to have a vapor-open building assembly, which means that walls and roofs should be constructed to dry, either on the inside, the outside, or both. As a result, water vapor ventilation should be taken into account. The cold side of the insulation must have a venting path in addition to a vapor barrier on the warm side of the envelope. This is due to the fact that no vapor barrier is perfect and that water may enter the building, usually as a result of rain. Generally speaking, less venting is needed the greater the vapor barrier and the dryer the environment.
Installing vapour barriers are an essential component when it comes to residential homes. Although often overlooked, the purpose of vapour barriers is to prevent water vapour from reaching basements, ceilings, attics, walls, or crawlspaces. If the water vapour was to enter these structures and condense, the building materials can start to rot or grow mold.
It is important that vapour barriers are installed correctly to protect the current building materials that are there.