Install a Subfloor with Tongue and Groove Boards Part 1

Plywood tongue and groove boards are used to build subfloors for houses and apartments. They resemble sheets of plywood with interlocking tabs and channels on the sides. The sheets are nailed or screwed in place across the floors joists. The subfloors are later used as the base for carpet, hardwood, vinyl, or tile flooring. Building your own subfloor is easy with the proper tools and materials. (This is Part 1 of a 2 part series. To move ahead to Part 2, click here.)

Prepare Room

The subfloor boards will be installed above the floor joists. If the joists have been heavily cut for wire or pipe runs, reinforce them with sister boards. Measure the area of the rooms you are flooring. Use a laser level and masking tape to measure off a level line around the perimeter of the room you are working in. Measure from the line to install a level floor. You will most likely use subfloor boards made from pine, do not use OSB.

Lay First Board

Mark from the wall to the joist with chalk and a pencil. Cut the board if it’s not 96 inches on center. Apply panel adhesive to the floor joists before laying the sheet into place. Lay a uniform bead. Tight joints in are the key to preventing squeaky floors, leaks or bowing drywall. The adhesive dries quickly so lay the sheet into place as soon as possible. The plywood may bow easily so use wood clamps or have a second person help you set the subfloor sheets in place.

Where and How to Nail

Fasten the subfloor boards in place using screws or nails. Screws can help you achieve a tighter fit which reduces noise. Local building codes govern screw placement but spacing them 6 to 8 inches apart along the edges of the board is the most common practice. Use an electric drill or screw gun to work quickly. Use decking screws rather than other types to ensure a tight grip. If you are installing double layers of plywood subfloor board, use a longer screw.

Cut and Lay the Other Boards

Apply a bead of subfloor adhesive all along the tongue and groove of adjacent boards. Use enough glue that when the boards are joined, some will squish out and form a seal around the joint. Push the boards together with the help of a partner. Kick them together or tap them with a wooden mallet. Leave a gap of approximately 1/8 of an inch for thermal expansion. Nail or screw up and down along the seam. Stagger the second course by laying the joints 48 inches off the center of the first course. Cut a 4-foot sheet to start the second course. For new construction, you can overlap the foundation and mark the excess with a chalk line. Then trim it off with a circular saw. For remodeling jobs, you will have to cut sheets to fit corners and irregular spaces.