Höyrynsuojarakenteet

Höyrynsuojarakenteet, known in English as vapor barriers or vapor retarders, are materials or assemblies used in building construction to prevent the diffusion of water vapor through walls, floors, and ceilings. Their primary function is to control moisture movement within the building envelope, thereby protecting the structure from moisture-related damage such as mold growth, rot, and material degradation.

The need for a vapor barrier depends on the climate and the specific construction. In colder climates, where the interior air is typically warmer and more humid than the exterior, vapor tends to move from the inside outwards. A vapor barrier placed on the warm side of the insulation (usually the interior side of the wall assembly) helps prevent this moisture from reaching cold surfaces within the wall cavity and condensing. Conversely, in hot and humid climates, where the exterior air is warmer and moister, vapor can move from the outside inwards, requiring a vapor retarder on the exterior side of the insulation.

Common materials used as vapor barriers include polyethylene sheeting, asphalt-coated kraft paper, and certain types of paint. The effectiveness of a vapor barrier is measured by its permeance, which indicates how easily water vapor can pass through it. Materials are classified into different classes based on their permeance values, with Class I vapor retarders offering the lowest permeance (virtually impermeable). Proper installation is crucial for the effectiveness of a vapor barrier, ensuring that all seams, penetrations, and edges are sealed to create a continuous barrier.