How to Lay Down Polystyrene (Eps) Sheets for Insulation

Attach a 6-mil polythene liner to the interior crawlspace stem wall, if you're insulating a crawl space. Use a water based adhesive as recommended by the manufacturer. Extend the edges of the vapor barrier on the ground, 1 to 3 feet from the wall, and at least 6 inches past the top of the wall and across the crawl space floor.

Measure and mark the desired cut lines on the polystyrene boards with a steel measuring tape and felt pen.

Extend the wall insulation at least 24 below exterior grade if the distance between the exterior grade level and the crawl space floor is greater than 24 inches. If the distance between exterior grade level and the crawl space floor is less than 24 inches, extend the insulating from the crawl space floor to the bottom of the wall.

Cut the polystyrene boards to size using a metal straight edge and utility knife. If the boards exceed 1 1/2 inches in thickness, use a small hand saw. Mark and cut the board to fit around utility pipes and service inlets where necessary.

Mark the nailing positions on the boards on approximately 2 foot centers vertically, and on 4 foot centers horizontally across the width of the boards.

Position the first board against the wall. Place a 1 inch nailing washer against the center mark and secure the board to the wall by driving a masonry nail through the hole in the washer with a power nailer. Repeat by using washers and nails to secure the rest of the board to the wall the same way.

Secure the remaining polystyrene insulating boards to the wall with closely butted vertical and horizontal joints as described in Step 6. Check with your local building code and allow the appropriate 2-inch to 3-inch bare termite inspection strips across the top of the wall if required.

Measure and cut 2-inch thick polystyrene panels to fit between floor joist. Mark and cut the boards to fit around utility pipes and service inlets where necessary.

Load the power nailer with wood nails. Nail the polystyrene boards to the crawl space floor through 1-inch washers between the joists as described in Steps 5 and 6.

Insulate all gaps between boards and around utility pipes and service inlets with a caulking gun loaded with the recommended foam insulating material.