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About Air, Vapour and Rain Barriers

air barriers help prevent moldAir movement through the wall assembly is far greater than many designers imagine.  With an air barrier system, you can improve a building’s performance and reduce heating and cooling costs by as much as 36%*

Air barrier systems help separate the outside environment from the desired interior environment.  Ultimately, an air barrier creates seamless continuity and structural integrity that helps eliminate uncontrolled air leakage and allows control over temperature, humidity, moisture and air quality throughout the building.  By not controlling potential moisture penetration, you increase the chance of mold growth and poor air quality.

>>Understanding air movement
>>Solving common building environment problems

What’s an air barrier?

An air barrier must first and foremost resist air leakage. Air leakage loads are significantly greater than most designers and architects realize. In the past, many materials were considered suitable air barriers, including building felt, concrete block, building wraps,and gypsum wallboard. A more enlightened understanding of the physics of air movement demands a more aggressive solution.

What’s a vapour barrier?

Vapour barriers limit the amount of water vapour diffusing through the wall as a result of different vapour pressures. With the advent of modern building science, it has been found that air leakage – and not vapour diffusion – is the real problem. In fact, air leakage accounts for over 200 times the amount of moisture transmitted by diffusion.**

What’s a rain barrier?

The function of a rain barrier is to keep liquid water from entering the building enclosure. Combined with flashing and other materials, the rain barrier ensures that there is a shingled assembly to direct liquid water to the exterior.*** A single material can function as the air barrier, vapour barrier (non-permeable air barrier), and water barrier.


* US Department of Energy – NISTIR 7238 Report
** R. Quirouetie. The Difference Between a Vapor Barrier and an Air Barrier
*** Air Barrier Association of America