Höyrynsulkuihin

Höyrynsulkuihin, often translated as vapor barrier or vapor retarder, is a crucial building material used in construction to control the movement of moisture vapor. Its primary function is to prevent water vapor from penetrating into building assemblies, such as walls and roofs, where it can condense and cause damage. This damage can include mold growth, rot, and degradation of structural components and insulation.

The effectiveness of a höyrynsulkuihin depends on its permeance, which is a measure of how easily water vapor can pass through it. Materials are classified based on their permeance ratings, with high, moderate, and low permeance. A vapor barrier, having very low permeance, is typically used in colder climates on the warm side of the insulation to stop interior moisture from reaching cold exterior surfaces. A vapor retarder, with higher permeance than a vapor barrier but still limiting vapor flow, may be used in different climates or applications where some vapor diffusion is acceptable or even desirable.

Common materials used for höyrynsulkuihin include polyethylene sheeting, foil-faced insulation, and certain types of paint or coatings. Proper installation is vital to ensure the integrity of the vapor control layer. This involves sealing all seams, penetrations, and edges to create a continuous barrier. The placement of the höyrynsulkuihin within the building envelope is determined by climate and the specific design of the wall or roof assembly to effectively manage moisture.