Why aren’t the vents in the crawl space working to keep it dry?

In this video, Chris explains to a customer in Parksville, BC why the vents that are supposed to keep her home’s crawl space dry aren’t working.

Crawl space vents are actually one of the biggest fallacies in terms of building science. Builders formerly believed that, by opening vents to the crawl space, the air would “circulate” within the area – come in from one vent and out of the other, thus helping dry out ground water evaporation – which they believed to be the only source of crawl space moisture.

Recent developments in building science prove that there are two problems with that line of thought:

1. Ground water is not the only source of moisture in the crawl space. The outside air, which gets into the crawl through the vents, also carries moisture in. During the summer, the warm, humid air will cool down inside the crawl space and the moisture will begin to condense all over the surfaces.
2. The air does not “circulate” within the crawl space. Because of a physics phenomenon known as “the stack effect”, the air in any building always moves upwards, towards the upper levels and then escapes through the roof and any openings at the top. As a result, air is sucked in from the bottom of the house through the basement or crawl space. This means that moisture in the crawl space is not being dried up; it is being carried into your living space, along with all the odors, mold spores and pollutants found in the crawl space.

In other words, crawl space vents not only fail to keep the crawl space dry, they actually are responsible for aggravating the moisture problem during the summer. During the winter, they are carrying cold air into your home, making your floors cold, your rooms uncomfortable and your heating system has to work much harder and consume more energy to keep up.