subject: The Basic Role Of An Air Barrier And Barrier Membranes In Commercial And Residential Building [print this page] With a growing focus on sustainable building, energy efficiency and durability have become important factors in building enclosure design. Use of continuous air barrier technology helps achieve both of these goals.
The most important use of air barrier membranes is to control airflow through the wall assembly. Air contains water vapor, so even a small air leak can allow large quantities of moisture into the wall assembly. This moisture intrusion can lead to wall structure problems such as decay, corrosion, loss of insulation value, mold growth and indoor air quality (IAQ). Protecting the assembly with an air barrier minimizes air infiltration into the walls.
In addition to controlling moisture content in a wall assembly, air barriers can improve the energy efficiency of a structure. The US Department of Energy (DOE) finds that up to 40% of the energy used to heat or cool a building is lost through air leakage. An air barrier membrane minimizes air leakage and can reduce energy costs. A 2005 study by the National Institute of Science and Technology (NIST) showed that energy savings of up to 40% could be achieved with a continuous air barrier. (add link to the study)
There are two types of air barrier membranes - vapor permeable and non-vapor permeable. Vapor permeable air barrier membranes allow moisture diffusion, providing an opportunity for incidental moisture that enters the wall assembly to dry out. Permeable air barrier membranes are recommended for mixed weather climates, which have both hot and cold seasons. Non-permeable air barrier membranes, however, do not allow vapor diffusion, thus acting as a vapor barrier. These air barrier membranes are most often used in climates that are either predominantly cold or predominantly warm.
Use of air barrier membranes is gaining ground while air barrier requirements are being incorporated into the energy codes of many states across the US. The National Building Code of Canada was the first to incorporate air barriers in 1986.
