What is an Air Barrier?An air barrier is any system of materials designed and constructed to prevent air from penetrating a building through the exterior walls. Air barriers come in a wide range of materials, including house wrap, liquid-applied membranes of various chemical compositions, nylon film, extruded polystyrene board, weather stripping, and built-up and self-adhered asphalt sheets. The air barrier system is the fundamental air enclosure boundary that separates conditioned indoor air from unconditioned outdoor air. These air barrier systems can be located on the exterior, interior, or between. The wall designers must assess the ideal location of the air barrier within the wall assembly and specify the proper type of air barrier to be used. Most air barrier types are durable enough to withstand knocks and handling during construction. While sometimes confused with vapor retarders, air barriers primarily restrict air leakage into and out of buildings and resist air pressure changes. This function helps to maintain a stable indoor climate. Moreover, air barriers secondarily prevent vapor from penetrating the exterior building walls. Vapor barriers, on the other hand, serve this function primarily. Air leakage loads may be significantly greater than most designers and builders realize. Therefore, a more informed understanding of the physics of air movement is vital in designing a more effective solution. By controlling air movement, air barriers provide substantial energy efficiency in buildings. Note the following critical issues regarding the application of air barrier systems:
- Air barriers can only be effective if installed continually over the entire building enclosure. Any penetrations and unsealed seams should be sealed appropriately.
- They should be impermeable to airflow and built to resist wind loads.
- They should be durable over the expected lifetime of the building.
- They must withstand the forces acting on them during and after their installation.