The Theory of Air Movement

Air leakage is the uncontrolled movement of air through the Building Envelope. This movement of air is caused by wind, stack effect and fan pressures. The combined forces are significant and must be resisted by the air barrier system. Uncontrolled air leakage translates into:

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

These issues have proven to be significant enough to effect building code changes. Air barrier technology is a rapidly growing concern for all designers and specifiers, and Bakor leads the industry with over 18 years of experience with successful, high profile projects.

With over 17 completely integrated systems, our architectural services team can assist building owners, designers and specifiers to create an effective plane of air tightness throughout the Building Envelope.

Theory on Air Barriers

The history of air barriers can be traced to the 1960's when it became obvious to researchers that air leakage into the wall and roofs was an important source of water migration. Moreover, during the energy crisis or the 1970's, building professionals were looking for ways to make buildings more energy efficient and eventually realized this could be achieved by stopping uncontrolled air leakage through the Building Envelope. The term "air barrier" was quickly adopted in the industry.

The main function of the air barrier is to prevent infiltration of outdoor air into a building and the exfiltration of indoor air to the outside. Air leakage can cause problems such as deposition of moisture in the walls, loss of heat and penetration of rain. Air can flow in and out of buildings through holes or joints in the envelope or through micropores in building materials. Bakor air barriers essentially plug all holes throughout the Building Envelope.

Air Barriers were first incorporated into the National Building Code of Canada in 1986. Today, designers must comply with Article 5.4 Air Leakage of the National Building Code of Canada. An air barrier must first and foremost resist air leakage. The loads involved are more significant than many designers realize. As stated in the code, materials intended to provide the principal resistance to air leakage shall have an air leakage characteristic not greater than 0.02 L/s.m² measured at an air pressure difference of 75 Pa.

Testing of air leakage is based on American Society for Testing of Materials (ASTM) E283, E330 and E2178. In these tests, a mock-up wall is constructed and covered with a membrane. The mock-up is then subjected to air pressures ranging from 75 Pa. to 3000 Pa. The air leakage through the membrane is measured at all pressure levels, and is inspected for visual delamination. All Bakor air barriers have been tested by independent testing laboratories.

Air barrier membranes can be categorized in the following two types of air barrier: Vapour Permeable or Non-Permeable.

1. Vapour Permeable Air Barriers:

Bakor vapour permeable air barrier membranes resist air leakage and rain penetration through the building envelope. However, since they are vapour permeable, they allow the diffusion of moisture, in the form of vapour. Therefore, they are not vapour barriers. In essence they can let the walls of your building "breathe". Vapour permeable air barriers offer designers more flexibility in the positioning of the air barrier within the wall assembly. Vapour permeable air barriers can significantly reduce the cost of exterior wall construction by allowing walls to be designed with a thinner profile.

2. Non-Permeable Air Barriers:

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

Refer to our vapour permeable air barrier or non-permeable air barrier web page for more information on the available Bakor air barrier membranes.