Höyrykalvon

Höyrykalvon, often translated as steam barrier or vapor barrier, is a material used in construction to prevent or control the movement of moisture in the form of water vapor through building assemblies. Its primary function is to mitigate condensation within walls, roofs, and floors. When warm, moist indoor air comes into contact with colder surfaces within the building envelope, water vapor can condense into liquid water. This trapped moisture can lead to a variety of problems, including mold growth, rot, reduced insulation effectiveness, and structural damage.

A höyrykalvon is typically installed on the warm side of the insulation in a building's thermal envelope, meaning it faces the interior of the building in colder climates where interior air is warmer and more humid than exterior air. This placement helps to keep the moisture-laden air from reaching the cold surfaces where condensation would occur. Common materials used for höyrykalvon include polyethylene sheeting, kraft paper facing on insulation, or specially formulated paints and membranes. The effectiveness of a höyrykalvon depends on its permeability to water vapor, which is measured by its permeance rating. A material with a low permeance is considered a good vapor retarder.

The need for and placement of a höyrykalvon can vary significantly depending on the climate, building design, and materials used in the construction. In very dry climates, a höyrykalvon might not be necessary or could even be detrimental. Conversely, in humid climates or in buildings with high internal moisture generation, a properly installed höyrykalvon is crucial for maintaining building durability and indoor air quality. It is important to consider the entire building envelope as a system to ensure that moisture is managed effectively.