Significant changes to air tightness requirements have been made in the 2012 IRC/IECC (as well as the new 2015 codes) — the new requirements are 3ACH50 for climate zones 3 through 8 and 5ACH50 for climate zones 1 and 2. A building's air tightness describes the degree of air leakage into and out of the thermal enclosure which separates conditioned space from the outdoors. Air leakage is the uncontrolled flow through the thermal enclosure due to pressure imbalances caused by wind, stack effect, and mechanical equipment. Air leakage in a building should be minimized because homes that are more air tight are more energy efficient. However, reaching the levels of these new requirements can be a challenge for builders and create design and performance issues.
The building’s air leakage rate is quantified by testing. The most common air tightness test is typically referred to as a “blower door” test. The test equipment consists of a calibrated fan, a panel to seal off the door, and a flow and pressure meter. For residential applications, the fan typically depressurizes the house to 50 Pascals at which point the air flow through the fan is recorded.
The TechNote provides builders with essential information on the topic of air tightness to help transition to the new codes and achieve compliance with codes and above-code programs. It points out the critical considerations essential to a smooth transition, including: