ångbarriärer

Ångbarriärer, also known as vapor barriers or vapor retarders, are materials used in building construction to prevent or slow the diffusion of water vapor through walls, ceilings, and floors. Their primary function is to control moisture within the building envelope. Water vapor is a natural byproduct of human activities like cooking, showering, and breathing, and it can also originate from the ground or outside air. If this vapor penetrates building materials and encounters a colder surface, it can condense, leading to a range of problems.

These problems include mold growth, rot, reduced insulation effectiveness, and structural damage. Ångbarriärer are typically installed on the warm side of the insulation in colder climates. This placement ensures that the vapor barrier is on the interior side of the wall assembly during the heating season, when the interior air is warmer and more humid than the exterior air. In warmer, humid climates, the installation strategy might be reversed or a more permeable vapor retarder might be used to allow drying to the outside.

Common materials used as ångbarriärer include polyethylene sheeting, certain types of paint, and specialized membranes. The effectiveness of an ångbarriär is measured by its permeance, which indicates how easily water vapor can pass through it. Materials are classified by the American Society for Testing and Materials (ASTM) into Class I, II, and III vapor retarders, with Class I being the most impermeable. Proper installation is crucial for ångbarriärer to function effectively, as gaps or tears can compromise their performance.