What is an Air Barrier?

Adam Hill

An air barrier is a membrane or a foam that is incorporated into the construction of a building in order to increase its lifespan and efficiency. Without an effective air barrier, heating and cooling costs can be significantly higher, and moisture can penetrate the walls of a building, leading to a number of potential problems such as mold. This is particularly the case in humid climates. Air barriers come in several forms, from mechanically applied housewraps, to polyurethane foam, which is applied by spraying.

Polyurethane foam can be applied by spraying.
Polyurethane foam can be applied by spraying.

The main purpose of an air barrier is to prevent air leakage between the inside and outside of a building, and sometimes even between areas of a building. Some estimate that a good air barrier can decrease heating costs by up to 40%, and cooling costs by up to 15%. Where air leakage is controlled, this can also allow for a smaller ventilation system, since less air will have to be conditioned. The reduction in cost from a smaller ventilation system alone can offset the cost of an air barrier installation.

Spray foam insulation is an air barrier that holds in heat and keeps out moisture.
Spray foam insulation is an air barrier that holds in heat and keeps out moisture.

While the movement of heat is slowed by an air barrier, this is not the only benefit offered. When air leakage from the outside is blocked, so are many of the pollutants carried by the air. Allergens, suspended particulate matter, water vapor, and smells from the street can all be blocked by an efficient air barrier. While water vapor is not generally considered a pollutant, it can have harmful long-term effects on buildings, by helping to facilitate the development of mold within building walls.

The corrosion of certain metal building components can also be sped up by the condensation of water vapor. While many air barriers do protect against water vapor, they should not be confused with vapor barriers. These, unlike air barriers, do not have to be sealed to prevent air leakage, and an occasional hole does not present a problem, as it would with an air barrier.

Apart from the practical benefits of using an air barrier are others, which are more difficult to quantify, but are every bit as important. Air barriers help a building's occupants feel more comfortable by eliminating drafts and reducing the inevitable spots of too-cold or too-warm air that result from the heavy use of heating and air conditioning. This can translate into better morale and higher productivity in a workplace, and a more comfortable and genial home environment, with the monetary savings as an added bonus.

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