Air Barriers – Another Wicked Important Part of Your Home

by Erik North on September 11, 2011

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Your home’s air barrier is that wall your sofa is pushed up against.

Thank you, good night!

Important note:
First thing…air ‘barrier’ is a bit of a misnomer (and an outdated term). Barrier implies totally stopping something. Air barriers in no way TOTALLY stop air flow but rather there are varying degrees of air permeability.

The physical space between the interior and exterior of your home is called the building envelope. This involves the physical structure, the thermal control layer, vapor control layer and air control layer defining the barrier between the in of doors and the out of doors.

The air barrier, also known as the air shell or the air control layer, around a home controls air movement and pressures. As you can probably imagine, air barriers are made of materials…air control materials. These materials have lower air permeance, either allowing, slowing or stopping the flow of, yes, air.

Why is this important? I mean besides that the air barrier keeps that nasty outside, non-home air out and cozy, warm inside air in?

First, because air can transport all kinds of, well, stuff. Water vapor, VOCs, chemical fumes can be transported by air movement. Properly built homes should control air movement so, say, air transported water vapor doesn’t condense on the inside of your roof deck. Things like that.

Second, your home retains the most heat and the thermal enclosure (that’s yer insulation) works best when it is paired with the air barrier. When there are gaps in the air barrier (obviously, a giant hole will lose you heat) or the air, vapor and thermal layers are spaced out (think a drop ceiling where air goes right past the ceiling and insulation) the insulation won’t work as well as it should.

Types of Air Barriers

There are several components to the air control layer. The air barrier accessories include adhesives, sealants, and primers for applying the air barrier. Air barrier components are the windows, doors and other egresses inserted and sealed into the building shell, creating a continuous barrier. Air barrier materials include physical shell materials (which include OSB siding, polyolefin wrap, closed cell spray foam or self-adhering exterior membranes) of a sufficiently low air permeability to control air flow. Air barrier systems combine air barrier assemblies, air barrier components and low permeable materials into an entire air control enclosure.

Energy Auditing and Air Leakage

Preventing excessive air leakage through the building envelope is really at the heart of energy auditing. It is the job of the air barrier to not only prevent excess air leakage, but to allow the flow of air that is most healthy and comfortable for the people living in the home.

When there are flaws in the air control layer, massive amounts of unconditioned air can enter your home (or conditioned air can escape). Close your eyes and imagine that blast of cold air on your next from a leak. Not fun!

In the end, my ultimate goal as your energy auditor is to encourage energy efficiency and comfort. When the air barrier is working with the vapor and thermal layers, you’ll save money and be more comfortable.

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