Dampfdiffusionsbremse

A Dampfdiffusionsbremse, often translated as vapor diffusion brake or vapor retarder, is a building material used in construction to control the movement of moisture in the form of water vapor through building envelopes. Its primary function is to slow down or prevent the diffusion of water vapor from warmer, more humid interior spaces to colder, drier exterior spaces. This is particularly important in colder climates to prevent condensation within wall or roof assemblies.

The term "Bremse" (brake) in Dampfdiffusionsbremse highlights its function of impeding the diffusion process, rather than completely stopping it. Unlike a vapor barrier, which aims for near-impermeability, a vapor diffusion brake allows a controlled, albeit slow, passage of water vapor. This controlled permeability is crucial for allowing any moisture that does enter the assembly to escape, preventing a buildup that could lead to mold, rot, or structural damage.

Dampfdiffusionsbremsen are typically installed on the warm side of the insulation layer in an exterior wall or roof. Common materials include specialized plastic films, treated papers, or membranes with specific vapor permeability ratings. The effectiveness of a Dampfdiffusionsbremse is measured by its vapor resistance (Sd value), which indicates the equivalent thickness of air layer that vapor would have to diffuse through. A higher Sd value signifies lower vapor permeability. Selecting the appropriate Dampfdiffusionsbremse depends on the climate, building design, and other materials used in the assembly.