A vapour barrier is a diffusion-inhibiting component layer that is intended to slow down the entry of moisture into another component in the form of water vapour.
According to DIN 4108-3, vapour barriers are defined as diffusion-inhibiting layers with an sd value (water vapour diffusion equivalent air layer thickness) of 0.5 to 1500 m. In contrast, vapour-tight vapour barriers (according to DIN: diffusion-tight layer) have an sd value of at least 1500 m. Typical areas of application for vapour barriers or barriers are on the inner (warm) side of roof insulation in order to prevent its moisture penetration by water vapour diffusion from the inside to the outside.
Vapor retarders are typically installed as foil or cardboard. Whether a vapour barrier or barrier must be used depends on the design.
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.
retarders 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. Particularly in wooden constructions, vapour barriers are preferred over vapour barriers.
Other typical areas of application are roof insulation for non-rear-ventilated flat roofs, which are covered with vapour-proof materials such as sheet metal coverings, flat roof foils and green roofs. (Check according to DIN 4108-3 whether a vapour barrier or brake is necessary !) For pitched roofs, modern moisture-variable vapour barriers are preferred to vapour barriers.
When processing vapour barriers, it is essential to ensure that the joints of the individual membranes are completely glued.
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