Foam boards are an option for insulating crawl spaces.
Foam boards are available in a variety of plastic blends and thicknesses that vary in how well they inhibit heat transfer, expressed as an R-value. Although not as good at reducing heat loss as fiberglass insulation, foam boards still provide adequate protection for crawl spaces, especially when those spaces require thinner insulation material due to space constraints. Choose foam boards for unvented spaces -- crawl spaces under the home that do not have vents near the top of the foundation. Insulate vented spaces with fiberglass batting against the subfloor.
Instructions
1. Line the crawl space floor with sheets of 6-mil plastic if the floor is not concrete. Purchase the plastic, which is sold in rolls, from home centers. Overlap each course by about a foot, and place bricks or stones on the overlap to prevent the plastic from curling up.
2. Paint the walls under the house with a vapor retardant, also available from home centers. This thick paint goes on with a brush or roller. Allow the product to dry completely before installing foam boards.
3. Insert a tube of adhesive into a caulk gun. Use a product that is designed for foam boards since some adhesives could melt the foam. Trim off the tip of the adhesive tube with a utility knife. Make the cut at a 45-degree angle at a point that creates an opening about 3/8 inch wide.
4. Cut foam boards to fit into the wall space, or turn them to face horizontally for walls that are at least 4 feet tall. A utility knife cuts through foam boards with two or three passes.
5. Squeeze the caulk gun trigger and apply long, even beads of adhesive to the back of a foam board. Use a wide arcing S pattern across the back of the board to cover it with glue.
6. Position the glued foam board into place, and press it to the wall with just enough pressure to create a bond between the adhesive and the wall. Too much pressure may compress and dent the foam. Hold the board in place for a minute or so to allow the adhesive to grab the concrete.
7. Repeat the process all along the walls under the home until they are all covered in foam boards.
8. Cover the seams between each panel with a tape made for sealing foam boards. The tape will cover gaps between boards where moisture enters or heat escapes.
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