DIY Rigid Foam Insulation

Measure the wall's height from the floor to the ceiling joists. Transfer this measurement to two pieces of rigid foam insulation, and place one mark on the left side and one on the right side of both pieces.

Lay a 4-foot level across the two marks. Use the level as a straightedge, and cut through the insulation pieces with a utility knife.

Transfer the same measurement from Step 1 to a 1-inch by 3-inch board. Cut the board to the appropriate length, using a handsaw.

Lift one piece of rigid foam insulation onto the wall and position it in one of the room's corners. Hold a 4-foot level against the insulation's side, and adjust the insulation so it is straight up and down. Place the second piece of insulation tight against the first piece. The two pieces' edges form a shallow gap. Lay the 1-inch by 3-inch board in the gap.

Drive masonry screws through the 1-inch by 3-inch board and into the foundation. Place one screw every 10 to 12 inches down the board's length.

Measure the wall from floor to ceiling, and transfer this measurement to another piece of rigid foam insulation and 1-inch by 3-inch board. Cut the board and insulation to this length.

Position the insulation against the last piece of insulation you installed and the 1-inch by 3-inch board in the shallow gap. Secure the board to the wall with masonry screws in the same way you did in Step 5. Continue on along the wall until you reach the opposite corner.

Measure the wall's height in the opposite corner. Transfer this measurement to a piece of rigid foam insulation, two 1-inch by 2-inch boards and a 1-inch by 1-inch square board. Cut all these items to the appropriate length.

Place the 1-inch by 1-inch board in the corner and secure it to the foundation with masonry screws. Lift both pieces of rigid foam insulation into the corner with their side edges pushed against the 1-inch by 1-inch board.

Put the 1-inch by 2-inch boards in the shallow gaps in the edges between the insulation and the 1-inch by 1-inch board. Secure the 1-inch by 2-inch boards in place with masonry screws.