How to Add a Basement Sub Floor

Adding a basement sub floor over the standard concrete slab has several benefits. Installing a basement sub floor creates a pocket for insulation between the slab and flooring, allowing you to heat the space more efficiently. Also, once the basement sub floor has been installed, you can add almost any type of flooring on top of it to finish the space.

Step 1: Clean the basement floor, making sure to remove any dust or debris.

Step 2: Add a layer of plastic sheeting to the concrete floor. Cut each sheet so the ends extend 6 inches onto the basement wall. Use construction adhesive to glue the sheet seams to the floor, and overlap each seam 3 inches. Also glue the sheet in place with construction adhesive so it extends up against the wall.

Step 3: Install a perimeter of 2x4 pressure treated studs against the walls of the basement. The studs should be on end, with the nominal 2 inch side against the basement floor and the nominal 4 inch side against the basement wall. Use a nail gun to secure the studs to the basement wall.

Step 4: Create a row of 2x4 pressure treated studs on the basement floor, spaced 16 inches apart. Hammer them into the perimeter pressure treated studs. If the area you are framing is wider than 8 feet, add a row of 2x4's to cap off the other end of the row.

TIP: To ensure that the floor is level, use a carpenter's level while installing the floor. If you find low spots, use wood shims to make up for the floor irregularities and raise the studs on the basement floor slightly.

Step 5: Continue adding rows of studs spaced 16 inches on center until the entire sub floor has been framed.

Step 6: Install insulation between the studs that make up the sub floor. Be sure to wear gloves and a face mask if you are working with fiberglass.

Step 7: Install a layer of 5/8 inch plywood over the studs and insulation. Hammer through the plywood into each stud below, spacing the nails about 10 inches apart.