How to Waterproof a Crawl Space

Waterproofing a crawl space can prevent mold and mildew growth. While some believe that venting the crawl space is the best option, others prefer to seal it to prevent any type of moisture from entering.

If you are having difficulties with your crawl space, take a look around the yard for areas that may be conducting moisture to the foundation. While there are a few small things you can do to prevent moisture accumulation, you may have to do some landscape and ground work to fully address any drainage problems before attempting to waterproof the actual crawl space.

Keep in mind that sealing the crawl space may cover areas that you will eventually need to access to conduct repairs. If you must break through the waterproof barrier, use a utility knife to make a clean cut. Then, after you have finished your repair, cut a patch out of plastic sheeting that is 6 inches bigger than the cut on all sides. Then tape together the cut, and put the new patch over the cut. Then attach the patch over the cut with duct tape as well.

Step 1: Make sure that the water from the roof is being directed away from the crawl space. This means that there should be downspouts that empty away from the crawlspace. You should also make sure that water from the yard does not sit next to the foundation: if it does you will have to direct it away from the area.

Step 2: Add plastic sheeting to the floor and extend it 8 inches up the wall of the crawl space, using a staple gun to secure the plastic sheeting to the wall. Tape any seams with duct tape and overlap them by 12 inches. Be careful not to pierce the plastic sheeting while installing it.

Step 3: Seal any vents leading to the crawl space. Use foam board and duct tape around the seam to create an airtight seal.

Step 4: Run a dehumidifier in the space if the air is particularly moist. To tell if you need to use a dehumidifier for a few hours, check for condensation in the crawl space after it has sat overnight.