Vapor barrier

A vapor barrier is a layer (usually the inside ) is mounted on the hot side of a component and hinders the diffusion of water vapor. You should prevent higher penetration of the insulation layer by diffusing water vapor. You can simultaneously assume the duties of the airtightness layer.

The moisture proofing technical design values ​​of individual building materials are defined in DIN 4108-4. The specified there approximate value for the water vapor diffusion resistance factor μ results with the layer thickness of the considered building material (in meters) multiplied by the so-called sd- value ( water vapor diffusion-equivalent air layer thickness or locking value ) of the device layer under consideration. This indicates the diffusion permeability or impermeability of a device layer.

DIN 4108-3 defines

  • Component layers with an sd - value of ≤ 0.5 m as permeable layer,
  • Device layers, with an sd - value of m is greater than 0.5 and less than 1500 as a diffusion inhibiting layer ( vapor barrier )
  • Component layers with an sd - value of m ≥ 1500 as a diffusion- tight layer ( vapor barrier).

Correctly, it would have in the products used in practice mostly hot vapor barrier, but the technically incorrect term vapor barrier has been found in the use of language use. Real barriers are only metal ( aluminum or copper foil) and glass. A vapor barrier (or brake) has to do with the room air only slightly. You must protect primarily components and structures from moisture.

Note

The vapor barrier is applied to the "hot" and the inside of the insulation must be made airtight. An improperly installed vapor barrier causes condensation water in the insulation level. Just a few leaks (eg, cable outlets, sockets, ... ) make a vapor barrier ineffective. Warm and humid indoor air into the insulation, cools down there, and the moisture contained in the air is reflected in the form of condensation down (condensation, dew point ). The insulating material can absorb water and thus lose insulating effect and the water can cause water damage and mold to the building fabric. The proper tightness of a vapor barrier is detected using a blower door test.

Indoor air quality
214094
de