Wow! Did last month's column ever generate a lot of interest. I've had a steady stream of calls since it was published. As promised, I will devote this column to describing how to properly seal the crawl space. It does work.
First of all, let me review with you the reasons why, in most cases, it is good to seal your crawl space. Moisture in the air always goes from warm to cool (like a glass of iced tea). Well, in the warmer months, 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 the ground for condensation to occur.
So, if the warm, moist air can get in through open vents, it will find a place to condensate and BINGO, there's your moisture problem. If you seal or close those vents, the warm, moist air can't get in your crawl space in the first place. And if you place heavy plastic on the ground, it will stop ground moisture (not standing water) from migrating into your crawl space.
However, let me stress that there are times when it isn't appropriate to seal a crawl space. In most cases it is the best option, but here are some situations when you should NOT seal a crawl space.
- Do NOT seal your crawl space if your state or local codes do not approve of this type of construction.
- In some cases, your pest exterminator might not approve and, if this is the case, do NOT seal the crawl space until you find another exterminator who will approve.
- Do NOT seal the crawl space if you are in a flood plain or if you ever have standing water under you house. You must solve the water problem first.
- Do NOT seal the crawl space if your dryer vent discharges into the crawl space. Change that and place the vent on an outside wall before you seal the crawl space.
- Do NOT seal the crawl space if you have combustible appliances, such as a gas furnace or a gas water heater, located in your crawl space. Such appliances require considerable amounts of air for combustion.
Now, if none of the above conditions exist, and you have decided to continue, here's the step-by-step method.
- From under the house, install two-inch rigid foam cutouts (eight inches by 16 inches) into the foundation vents.
- Install a minimum of eight-mil plastic across all of the ground of the crawl space and tape and/or overlap the plastic's seams.Install the plastic about six inches up the foundation wall. This will allow you to spray cellulose or foam insulation on the foundation wall. Once again, make sure you let your exterminator know about your plans before you seal the crawl space.
Folks, that's really about all there is to it. Many will tell you that sealing up a crawl space will cause moisture problems. The fact is, when we are called to solve moisture-related problems in a crawl space, we solve these problems as I described here in this column. When the crawl space is sealed, there should be no moisture in the space unless you have a plumbing leak. While this rarely happens, you may want to install a small sump pump at the lowest elevation in case a leak develops.
In my honest opinion, this is how you should treat your crawl space. By sealing your crawl space, you will have a drier area with a more constant temperature, which will also help you save on your utility bills. And as always, feel free to call me at the office at 501-653-7931 if you have other questions.