You can install laminate, engineered wood, resilient flooring, and many other finished flooring materials directly over a dry concrete slab. However a wooden subfloor helps insulate the flooring from the cold concrete. It also adds a little cushion to the hard surface of the concrete. A wooden subfloor will not cure moisture problems. Moisture that comes up through the slab will ultimately find its way into your finished floor. Cure the moisture problem before you install the floor.
Headroom, especially in a basement, may be at a premium. To make low flooring framing that will conserve headroom, lay pressure-treated 2x4s (sleepers) flat and cover them with 3/4-inch tongue-and-groove OSB underlayment or exterior plywood.
Typical Sleeper Subfloor Installation
What You Need
- Circular saw
- Powder-actuated gun
- Cordless drill
- Polyethylene membrane
- Powder-actuated fasteners
- 3/4-inch tongue-and-groove OSB underlayment or exterior plywood
- Pressure-treated 2x4s
Step 1: Prep Floor and Mark Placement
Prepare the floor by vacuuming and installing a waterproofing membrane on asphalt mastic. Overlap the seams of the plastic sheet at least 6 inches and tape the seams with the tape recommended by the manufacturer. Starting with a 1/4-inch gap along the walls, mark the sheet with a felt marker at 16-inch intervals. Snap chalklines to help you position the sleepers. Set out the sleepers along the perimeter of the room and in their approximate locations across the rest of the floor, cutting them to length as necessary.
Step 2: Level Sleepers
After making sure that the floor is level, use cedar shims to level the sleepers. Lay a 4-foot level across the sleepers to make sure they lie on the same plane. Insert cedar shims to raise the sleepers at low spots. Fasten the sleepers (through the shims) with powder-actuated fasteners.
Step 3: Start Underlayment
Set the first sheet of underlayment (tongue to the wall) with the long side perpendicular to the sleepers and 1/2 inch from the wall. Fasten the sheet with 2-1/2-inch coated screws every 6 inches along the walls and every 8 inches across the sheet. Don't drive screws at the grooved edge yet.
Step 4: Finish Underlayment
Install the remaining sheets in the first row along the wall with a 1/8-inch gap between the ends. In the second row start with a half-sheet (then a full sheet for the third row) so the joints will be offset. Fit the tongue of one sheet into the groove of the other and screw it to the sleepers.