We all know about how stack effect works in homes, but during presentations, I’m always surprised by how many hands are raised in response to the question: “How many of you think you can make a house too tight and cause problems with indoor air quality?” Generally, at least three-quarters of the room raises their hands. Really? My colleague Joe Kuonen says that getting a house so tight that you need to ventilate is a feat worth celebrating. “Now, we can get fresh air from a place we can trust,” he says. Where do most of our homes get their fresh air? From places we cannot trust, like crawl spaces.