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Green Basics

Air Barriers

An Air Barrier Is an Essential Part of the Building Envelope

ABOUT AIR BARRIERS Save energy and protect moisture damage Building scientists have learned a great deal about air barriers since the 1970s. They now recognize that air barriers are key to how long a building will last, how much energy it will require to heat and cool, and how comfortable its occupants are going to be. In high-performance houses, few building components are more essential, and building and energy codes have become much more stringent. As a result, houses built to code now must be relatively tight. Building a house to the Passivhaus standard is impossible without a carefully detailed air barrier. Getting rid of unwanted air leaks accomplishes three essential goals: Saving energy (reducing the cost of heating and cooling the house). Limiting the amount of moisture that is carried into wall and roof cavities, thereby reducing potential damage caused by moisture. Controlling the source of fresh air that’s brought into the house, keeping air quality high. There is no single method, and no single material, that makes an effective air barrier. Instead, air barriers are really a number of different materials that work together. Everything from caulk and spray foam to rubber gaskets, drywall, housewrap and sheathing can be part of the mix. What counts is how these materials are installed. The success or failure of the air barrier depends largely on a number of tradespeople understanding how an air barrier works, and their role in ensuring its integrity. Although there are lots of ways of getting to the same goal, there are two rules of thumb that apply: the air barrier should be next to the insulation layer, and it should be continuous. Air barriers are not vapor barriers Vapor barriers and air barriers serve two different functions. Vapor barriers stop (or at least slow down) moisture…

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