ABOUT AIR MOVEMENT & AIR BARRIERS

Air Barriers Systems are a component of building envelope systems that control the movement of air into and out of buildings. A properly functioning air barrier system provides a barrier against the intrusion and diffusion of air due to air, wind, stack and vapor pressure into and out of buildings. Air leakage from an interior building environment (exfiltration) causes the HVAC system of a building to consume extraneous energy in order to produce more conditioned air than would be required in a building that has a properly functioning air barrier system. Conversely, a building envelope system that allows air infiltration due to air, wind, stack and vapor pressure into the interior building environment causes the HVAC system of a building to also consume extraneous energy in order to maintain the desired interior temperature and humidity levels. The use of barrier systems in building construction will result in building energy cost savings as well as reduce the amounts of air born pollutants which result from the combustion of energy producing fuels. Pollutants contribute to "The Greenhouse Effect" which increases both Global Warming and the deterioration of the Earth's ozone layer.

The United States Department of Energy has concluded that up to 40 % of the energy consumed to heat or cool a building is due to air leakage into and out of buildings. A properly installed air barrier system will substantially reduce the amount of air leakage of a building envelope system thus reducing the building's energy consumption.

Air Barrier Systems also protect against premature corrosion of metal stud back-up systems as well as other metal components in building envelope systems. Air flow has the ability to transport exponentially more moisture into and through the building envelope system than occurs through vapor migration alone. This transport of moisture can also cause any of the following problems:

• Uncontrolled heat loss
• Uncontrolled cooling costs
• Increased humidification needs
• Condensation problems
• Mold and serious indoor air quality concerns

Air Barriers Systems can be categorized in the following two types: Vapor Permeable or Non-Permeable.

Vapor permeable air barriers:

Vapor permeable air barrier membranes resist air leakage and rain penetration through the building envelope. However, since they are vapor permeable, they allow the diffusion of moisture, in the form of vapor. Therefore, they are not vapor barriers. In essence they can let the walls of your building "breathe". Vapor permeable air barriers offer designers more flexibility in the positioning of the air barrier within the wall assembly.

Non-permeable air barriers:

Non-permeable air barrier membranes resist air leakage, rain penetration and vapor diffusion. Therefore, they act simultaneously as an air barrier, a vapor barrier and a rain barrier. Since these membranes also act as a vapor barrier, the positioning of non-permeable air barriers within the wall assembly is critical in avoiding potential condensation problems.

The Bottom Line:  The benefits and energy cost savings of incorporating air barrier systems into building envelopes far outweigh and offset the initial cost of installing these systems.

For additional information about air barriers go to http://www.airbarrier.org/index.htm or http://www.henry-bes.com/airbarriers.asp