A vapour barrier is a diffusion-tight component layer that prevents water vapour from penetrating other components and thus prevents moisture damage. The classification into the categories vapour barrier and vapour barrier is regulated in DIN 4108-3. Accordingly, vapour barriers are defined as diffusion-tight layers with an sd value (water vapour diffusion equivalent air layer thickness) of at least 1500 m. For the less diffusion-tight vapour retarders (DIN 4108-3:diffusion-inhibiting layer), the sd value is between 0.5 and 1500 m.
Vapour barriers are usually made of aluminium-clad plastic films, bitumen welding membranes, bitumen roof waterproofing membranes or polyethylene films. Mesh meshes significantly increase the tear resistance of vapour barriers.
The requirements for the sd value of a system-compatible membrane can be created or checked with the help of a diffusion calculation according to DIN 4108, Part 3, Section A6.
Vapour barriers must always be installed on the inner (warm) side of a wall structure in order to prevent moisture penetration by water vapour diffusion from the inside to the outside.
Typical areas of application are roof insulation for non-rear-ventilated flat roofs that are covered with vapour-proof materials such as sheet metal coverings, flat roof foils and green roofs. In the case of pitched roofs, vapour barriers are hardly used anymore because of the possible moisture damage in the event of damage to these membranes and the development of new products (e.g. moisture-variable vapour barriers).
When processing vapour barriers, it is therefore essential to ensure that the joints of the individual membranes are completely glued.
☛ flat roof - vapour barrier and vapour barrier
☛ pitched roof - vapour barrier and vapour barrier
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