How do you insulate a crawl space?

Insulating the walls of a crawlspace with waterproof insulation offers a better option than insulating the areas between the floor joists, as wall insulation keeps floors warm and protects plumbing. The job is labor intensive and requires working under the home. It requires rigid foam insulation, several cans of spray foam insulation, a plastic vapor barrier and tape.

1. Eliminate moisture problems

   Before beginning the insulation process, eliminate any moisture problems from the crawl space. Make sure downspouts extend to direct water away from the foundation. Maintain the soil to ensure it slopes away from the foundation.

2. Apply rigid insulation to walls

   Rigid insulation is easier to install than unfaced fiberglass batts. Apply using construction adhesive.

3. Seal vent openings

   Vent openings allow accumulated moisture to evaporate from the crawlspace. After solving the moisture problem, the crawl space does not need them. Close the vents and apply a commercially available vent cover to prevent cold air infiltration to the space.

4. Fill the gaps

   Cut smaller pieces of rigid foam to fill the area between floor joists. Seal any remaining gaps in the rigid insulation with a spray foam product.

5. Install a vapor barrier

   Install a plastic vapor barrier on the floor of the crawl space. Attach the plastic to the rigid foam using tape.