Ångtätsbarriärer

Ångtätsbarriärer, often referred to as vapor barriers or vapor retarders, are materials used in building construction to control the diffusion of water vapor. Their primary function is to prevent moisture from migrating through building assemblies, such as walls and roofs, and condensing within the structure. Condensation can lead to a variety of problems, including mold growth, rot, and reduced insulation effectiveness.

These barriers are typically made from materials like polyethylene sheeting, aluminum foil, or specialized coatings. Their placement within the building envelope is crucial and depends on the climate zone. In colder climates, vapor barriers are generally installed on the warm-in-winter side of the insulation, effectively the interior side of the wall or ceiling. In warmer, humid climates, they might be placed on the exterior side or omitted altogether, as outward moisture movement can be more problematic.

The permeability of a material to water vapor is measured by its permeance, often expressed inperms. Vapor barriers have very low permeance, meaning they significantly restrict vapor movement. Vapor retarders are a broader category that includes materials with varying degrees of permeance, from impermeable (Class I) to semi-impermeable (Class III). The appropriate type and placement of an ångtätsbarriär are determined by building codes, climate conditions, and the specific design of the building to ensure long-term durability and occupant health.