What does sealing a crawl space have to do with energy savings? Actually, a lot, as you'll soon see. In fact, one of the most asked questions I get has to do with crawl spaces. It goes something like this. "Mr. Rye, how do I prevent moisture, mold and musty smells in my house's crawl space?"
A common answer to this question is to add more foundation vents. But nothing could be further from the truth, my friends. If that was the answer you got, then the person who advised you simply didn't know the facts. Now I'm assuming that you don't have standing water under your house, which is another serious topic. (Call me if you have that problem.)
Twenty-five years ago, I was working with Steve Hudson, a geothermal system installer who lives in north Arkansas. Steve had previously introduced me to blower door testing of houses, which is the best way to determine the energy efficiency (or inefficiency) of a house. He had also been trying to convince me that we should be totally sealing crawl spaces and NOT installing foundation vents. I thought he was crazy.
I recall that the day was cold and snowy and he asked me if I would go to his house and look at his crawl space. I really wanted to head back home to Little Rock, but I agreed to go.
We trekked through the snow to his house and opened the crawl space access door. Remember, it is cold and snowing, probably about 25 degrees. I will never forget what I saw. I expected to find a dark, damp dirt floor with no telling what growing on the ground, walls and floor joists. Instead, I was pleasantly surprised when he turned on a light, revealing clean white plastic on the ground and white cellulose insulation that had been sprayed on the foundation walls. Most importantly, the crawl space was as warm as toast and as dry as the desert.
My first thought was, "this is wonderful." My second thought was, "surely I can't be wrong." Well, I was wrong. I started telling everyone about sealing up crawl spaces. And then everybody thought I was crazy.
One day it dawned on me that if a crawl space is sealed at the ground and it has no foundation vents, then it is really like a basement, only not as tall. So why not treat a crawl space just like it is a not-so-tall basement.
It also dawned on me that most folks close their foundation vents in the winter. That rarely, if ever, causes a problem. Then they open the vents in the summer when the outdoor air is most humid. Moisture in the air always goes from warm to cool (like a glass of iced tea). Well, the crawl space is cooler than the hot humid air, which means that the warm moist air is trying to find a cold surface, like ductwork, floor joists or ground for condensation to occur.
Read this closely now. Moisture in a crawl space comes from only three sources:
- The ground
- Outside air
- Or from a plumbing leak
If you place heavy plastic on the ground, it will stop ground moisture (not standing water) from migrating into your crawl space.
If you close or seal the foundation vents that prevents outside moisture from entering the crawl space. And if you don't have a plumbing leak, you don't have a plumbing leak. BINGO. No moisture. No mold. No musty smell. A warmer floor in the winter. And, oh yes, as proven by research, a 10 to 20 percent savings on your heating and cooling costs.
So, how exactly do you seal off the crawl space, you ask? I'll give you specific details on that next month. In the meantime, feel free to call me at 501-653-7931 with any energy savings questions you may have.