Rigid foam insulation offers a thermal resistance between R-5 and R-8, roughly twice that offered by traditional batt insulation. Install these panels over wall or ceiling cavities, including those filled with existing fiberglass batts, to boost the R-value and improve home comfort and efficiency. Plan to cover your new foam insulation with drywall to improve fire resistance and comply with building codes.
Cut panels to fit using a box cutter or snap-away utility knife. Use a straight edge or T-square to guide your cuts.
Position the first foam panel perpendicular to the wall or ceiling framing.
Hold the foam in place while you use 2-inch ring-shank nails to fasten the board to the framing. Use a nail every 12 inches along each edge. The plastic cap of the ring-shank nail prevents the head from sinking into the foam.
Butt the next panel tightly against the first without overlapping. Use ring-shank nails to secure it to the stud every 12 inches. Repeat to cover the entire wall or ceiling.
Tape seams using building paper tape or tape designed for foam insulation. The tape helps minimize air leaks, further improving the efficiency of the home.
Install 1 by 3 furring strips over the insulation panels on top of each stud. The furring strips should run vertically from floor to ceiling, or from eaves to rafters, if you are installing them on a sloped ceiling. Use 2-1/2 inch deck screws to drive the furring strips into the foam and the wood framing beyond. If the foam is being compressed around the head of the screw as it enters the wood framing, you may need to pre-drill holes in the furring strips. Any compression reduces the effectiveness of insulation. Pre-drilling can also help prevent furring strips from splitting.
Position sheets of drywall over the furring strips and fasten them every 12 inches using drywall screws. Cut drywall to fit as needed using a sharp utility knife.
Tape the seams in the drywall using drywall tape and finish the walls as desired. You may wish to leave the walls unfinished if they are located in the attic or an unoccupied area.