Foundation vents can do more harm than good

If you are supposed to seal up a crawl space and stop humid air from coming in, then why do they build vents on homes? As an inspector, I think this is the most common question I get asked by homeowners. Usually a homeowner is trying to understand the whole process when they ask. It falls on the inspector to teach every homeowner why encapsulating and drying out the crawl space is a good idea.

I had a homeowner once that asked me about the vents with a completely confused look on her face. I started by assuring her that we, as an international network of companies, have seen amzing results by using the CleanSpace system. I also told her that it is important to remember that most unexplainable housing questions are because of building codes and it's best to avoid thinking about the reasoning behind the rule.

The idea behind foundation vents comes from trying to clean out the musty air under a home. When a nice breeze is blowing outside it is supposed to hit those vents with such force that it blows the old air through the crawlspace and out the vents on the other side. I have been in many crawl spaces with open vents and I can tell you that it just doesn’t happen. There is also a theory that says cold air doesn’t hold as much moisture as warm air. This is why we are supposedly supposed to “open the vents in the summer and close them in the winter.” What’s even worse is seeing powered vents in crawl spaces. These things are meant to draw air in and keep it circulating throughout the space. Try putting your hand up against one of those vents, see if you feel a powerful gust of air - I know I never have. They also require additional electricity and won't help at all.

As I’ve said before, a crawl space is basically a short basement, and I almost never see basement windows open at any time of year. When we close off the vents and seal them up we are eliminating the problem of moist air entering a crawl space in the first place. If you want to avoid wood damage, mold, and other issues it's important to seal off the outside air and keep the crawl space dry.