Either approach requires that the slab be prepared before you begin. It should be in good condition, free of excess moisture and level.
- Insulating concrete garage floors 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.
- Lay sheets of rigid-foam over the polyethylene. 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. Tape the seams with heavy-duty construction tape.
Be sure to use compression-grade rigid-foam panels, which are typically installed beneath concrete slabs. Check with your supplier or the manufacturer for advice on the best thickness and R-value to use.
- Lay 1/2-inch plywood over the foam, running the sheets perpendicular to the long dimension of the foam. Space the panels 1/4 inch apart, with a 1/2-inch gap around the perimeter.
- Add a second layer of 1/2-inch plywood, running this one perpendicular to the first, with the same spacing.
- Fasten the two layers of plywood together with 7/8-inch screws or staples. After insulating the concrete floor, install the finish flooring.
What You Need
- 6-mil polyethylene
- Rigid-foam insulation (compression grade)
- Heavy-duty construction tape
- Utility knife
- 1/2-inch plywood
- Circular saw
- 7/8-inch screws or staples