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Air Leakage

A blower door tests the tightness of the home’s envelope by pressurizing or depressurizing the structure and then measuring the amount of time for the entire air supply in the house be replaced with fresh air. For the NAHB’s Field Demonstration of Alternative Wall Insulation Products study, four builders insulated different houses with the various insulation materials. Their summary noted the following:

  1. Better caulking, window foam and other air barrier improvements generated the most improvement in the building envelope – in fact, a large measured difference between batt insulated houses was found, when one used improved air sealing techniques and the other did not.
  2. Neither the Blow-in-Blanket System (R14.7) nor cellulose (R12.6) measurably reduced air leakage but
  3. While foam in place (R12.6) had the lowest air leakage, the results were variable when uncoupled from air sealing techniques.

So, where does that leave us? The most important thing is that whatever insulation you use, the details are the most important thing. Paying attention to where air can come into the home is the easiest way to create a more comfortable home – or create headaches later if you don’t. The other important thing to remember is that every insulation system can stop uncontrolled air. Just as the house is a system, your insulation is one too.
