Either approach to garage floor insulation requires that the slab be prepared before you begin. It should be in good condition, free of excess moisture and level.
- Installing garage floor insulation begins with covering the entire floor with 6-mil polyethylene, which will serve as a vapor barrier. Overlap the seams about 6-8 inches. Run the polyethylene up the sides of the walls 3-4 inches. Tape the seams with heavy-duty construction tape.
- Lay pressure-treated 1x4 or 2x4 sleepers flat around the perimeter of the garage, leaving a 1/4-inch gap between sleepers and the wall. Fasten the sleepers to the slab with a powder-actuated nailer (check a tool rental outlet if you don't own or can't borrow one). Install sleepers on the rest of the floor, centered every 12 inches (for 1x4s) or 16 inches (for 2x4s).
Plan to use 2x4s for sleepers unless you need to restrict the height of the finished floor. The thicker sleepers will create a sturdier floor.
- Use rigid-foam insulation that is the same thickness as your sleepers. Cut the foam just wide enough to fit between the sleepers, then lay the strips in place. Use a utility knife to cut the foam to size (a hacksaw blade or drywall saw also work well). Leave a 1/4-inch gap around the perimeter.
Be sure to use compression-grade rigid-foam panels for garage floor insulation, which are typically installed beneath concrete slabs.
- Attach a layer of 3/4-inch plywood perpendicular to the sleepers. Fasten the plywood to the sleepers with ringshank nails (1 1/4-inches for 1x4 sleepers, 2-inches for 2x4 sleepers) or comparably sized galvanized screws.
Stagger the edges of the plywood panels. Install the finish flooring over the garage floor insulation.
What You Need
- 6-mil polyethylene
- Heavy-duty construction tape
- Lumber for sleepers (pressure-treated 1x4 or 2x4)
- Powder-actuated nailer
- Rigid-foam insulation (compression grade)
- Utility knife
- 3/4-inch plywood
- Ringshank nails or galvanized screws