kosteussulkua

Kosteussulkua, or moisture barrier, is a continuous layer in building envelopes designed to limit the diffusion of water vapor through structural assemblies. It is used to reduce moisture migration from occupied spaces into insulation, timber, and other structural components, where condensation can lead to mold, decay, or decreased insulation efficiency. Kosteussulkua is typically implemented as a thin sheet or membrane, such as plastic film, foil-faced laminate, or self-adhesive membrane.

Placement and function: In heated buildings in temperate and cold climates, the barrier is usually placed on the warm side of the insulation. In Finland and other cold climates, it is commonly installed on the interior side of wall and roof assemblies to minimize vapor entry into the cooler structural layers. Some assemblies use diffusion-open vapor retarders to permit drying; in such cases the material's permeance is chosen to suit climate and risk of condensation. The joints and penetrations must be continuous and well sealed to be effective.

Materials and installation: Common materials include polyethylene sheets, foil-faced laminates, and self-adhesive vapor barriers. Perimeter joints are sealed with compatible tapes or sealant, and penetrations for electrical boxes, pipes and outlets are carefully flashed. The barrier should not be punctured or displaced during construction, as even small gaps can create paths for moisture.

Limitations and relationship to other moisture controls: A moisture barrier is one element of a moisture management strategy that also includes ventilation, insulation continuity, and drainage. It is not a substitute for an appropriately designed ventilation system or for a breathable, diffusion-open assembly where drying to the exterior is required. Improper installation can trap moisture between layers and promote mold or wood decay.

See also: vapor barrier, air barrier, diffusion open membrane, building envelope.