Do building scientists sometimes wake up and feel like Bill Murray in “Groundhog Day,” trapped in a time loop where no matter how many times they try to explain the importance of air-sealing nobody listens? It must have seemed that way at times, but builders and building codes are gradually heeding their advice and houses are slowly but surely getting tighter—and the result is lower heating and cooling bills, healthier indoor air, and more durable structures.
A certain level of air tightness is now required by the International Residential Code. In Climate Zones 1 and 2, the air leakage rate in new houses should not exceed five air changes per hour at a pressure difference of 50 pascals (ach50) when measured with a blower door; in Climate Zones 3 through 8, the limit is 3 ach50. Conscientious builders will be the first to say these limits are not a big deal. But it gets harder when the goal is certification under a more stringent program. The German Passive House standard, for example, requires an air leakage rate of no more than 0.6 ach50, and builders and owner/builders who try to hit this metric can spend a lot of time finding and plugging even tiny air leaks in the building enclosure.
What is a reasonable goal? A 2013 study by the Lawrence Berkeley National Laboratory concluded that the 5 ach50 and 3 ach50 guidelines are a good middle ground that would save U.S. consumers about $33 billion a year in energy bills. Lower leakage rates will, of course, save more money but are more difficult to achieve.
As more builders get serious about reducing air leaks, manufacturers have responded with a greater variety of products. Some of them are more expensive and finicky than others, but if a builder wants to produce a house that’s close to airtight, he…