In this video, This Old House general contractor Tom Silva explains the wide world of spray-foam insulation.
Tips for Selecting and Using Foam Insulation
Pro Tip: As Tom Silva of This Old House has noted, low-density polyurethane spray foam is the insulation technology to beat. It forms a lock-tight bond with studs and sheathing that blocks all air movement, it flexes enough to accommodate seasonal wood movement, and it retards moisture passage.
- Pick the appropriate foam insulation for the job at hand. Shake can well before applying.
- Use minimal-expanding Window-and-Door Foam to insulate around windows and doors.
- Apply the foam sparingly, allowing it to expand to fill the gaps.
- Use Gap-and-Crack Foam to fill spaces between the house foundation and mudsill.
- Spray foam insulation behind electrical boxes prior to insulating the walls with fiberglass batts.
- Use fire-block foam insulation to fill holes around pipes, electrical cables, and ducts.
- To insulate large areas, such as stud bays, use two-part polyurethane spray foam.
When insulating around windows, apply a single thin bead of minimally expanding polyurethane foam to the gap between the window and the framing, and allow the bead to expand and cure for one hour before adding more. Repeat until the cavity is completely filled. Do not fill the gap between the jamb and framing with too much foam too quickly — otherwise, the jamb could bow and bind the sash. If the gap is too narrow for either foam or fiberglass insulation, seal it with a bead of caulk.
Triple-expanding gap fillers are fine for masonry, which can withstand the pressure the foam exerts as it cures. For doors and windows, however, always use a flexible, minimally expanding foam, which won’t bow jambs out of shape. If a used can of foam isn’t empty, you can store it upright in a cool place for up to two weeks — but first, unscrew the trigger and nozzle and clean out any hardened foam with a straightened coat hanger.
