Know Your Air Barrier

What is an Air Barrier?

Air Barriers are materials that control the movement of air into and out of a building. A number of air barrier materials and components that work together are called air barrier systems. The air barrier system is part of the building envelope. Typically, the building envelope divides the interior environment from the exterior environment, or dissimilar environments. The air barrier is an essential part of the building envelope, by providing the control of air into and out of a building. This system essentially "wraps" the building's shell and ensures that it protects the building from the effects of air leakage. Air Leakage can have detrimental effects on how a building functions and reduces the life span of a building.

Quite Often, there is confusion between air barriers and vapour barriers. A vapour barrier's primary function is to stop the transmission of moisture by diffusion through a material. An example of a vapour barrier is Polyethelyne. At times, materials can be deemed an air/vapour barrier, in which the material is designed to stop both the movement of air and vapour diffusion.

Air Barriers can be placed anywhere in the building envelope. Vapour Barriers must be placed on the warm side of the insulation. An Air/Vapour Barrier must also be placed on the warm side of the insulation.

Most materials used in construction today provide both the air barrier and vapour barrier. These materials come in the form of sheet membranes, spray-on systems, sheet metal, etc.

The majority of problems in a building are due to premature degradation of components. When moisture is transported into the building envelope through air leakage and is subjected to different temperatures and time periods, it can cause the rot of envelope components, rusting and degradation of structural supports, and damage to exterior finishes. The cost to repair buildings with these problems is approximately 50 times higher than doing the proper application to begin with. It is estimated that 90 % of damage to buildings is caused by moisture. Moisture transport by air leakage is estimated to be 60 times greater than transport of moisture by diffusion. The control of air movement is essential.

It is very important to have a functioning air barrier system in the building envelope. An air barrier contributes to both a reduction in heat loss and the reduction in the transport of moisture into the envelope. This will make a building more durable, energy efficient, comfortable and safe. It will also reduce the effects of greenhouse gas emissions and the production of C02 by making the building consume less energy.

Improper air barrier application can cause a decreased building life cycle, indoor air quality problems, lack of comfort and safety for building occupants, and high operating and energy costs.