The comfort, efficiency and health benefits of a tightly sealed home have been well documented in recent years, garnering attention from organizations like the American Lung Association and Energy Star. Traditionally, homes have been built to “breathe,” a concept emphasizing the exchange of air between a home and the outside environment. Now, construction methods are aimed at reducing this occurrence as much as possible, an objective driven by lowering a home’s air exchange rate. These rates are designated as Air Changes per Hour (ACH) and can be denoted at 50 pascals of pressure or at “normal” conditions (ACH50 or ACHn, respectively).
In response to the new paradigm, the 2009 International Energy Conservation Code (IECC) put the maximum allowable “breathability” of a house at 7.0 ACH50, which is about 0.35 ACHn or one air change every three hours or so. To improve on that, IECC 2012 has constrained the air tightness requirement to 5.0 ACH50 (0.25 ACHn; one air change every four hours or so).