Air Barrier Functions And Benefits

Uncontrolled air leakage could negatively impact building occupant comfort, durability of building materials, and energy consumption levels. Air barriers play a critical role in controlling these effects of air leakage.

The primary function of an air barrier is to control air leakage in order to avoid undesirable consequences.

Consequences of Air Leakage through the Building Enclosure

Consequences of Air Leakage through the Building Enclosure

Air movement can create drafts affecting thermal comfort, or carry contaminants and moisture through the building enclosure, affecting indoor air quality and safety of the occupants. Excess moisture can also condense on interior surfaces and cause premature degradation of building materials, such as corrosion of metal and rotting of wood. Unintentional air leakage could lead to increased energy use in at least three different ways: over sizing of HVAC equipment to compensate for the heating and cooling loss through air leakage; loss of effective R-value due to wetting of thermal insulation by moisture transported through air currents; and loss of effective R-value due to convective loops, also known as the wind-washing effect.

In addition to their primary function, air barriers can protect against water intrusion, in which case they are air and water resistive barriers. Some air barriers also control vapor diffusion, in which case they are air and vapor barriers. Air, water and vapor barriers play a critical role in managing air and moisture movement through the building enclosure. "Unfortunately, there is still confusion on the functionality associated with different barrier membranes, especially when a single membrane performs multiple functions," says Spinu, noting that the most common confusion is between air barrier and vapor barrier functions. "While air barriers can and should be used in all climates, vapor barriers are climate specific," she adds.

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