How to Fix a Rotted Subfloor Under a Wall

Take any furniture and appliances out of the room near the rotted subfloor. Cover appliances and furniture left in the room with plastic, ensuring the furniture and appliances are fully covered, and tape down the edges of the plastic.

Break the paint at the top of the trim around the bottom of the wall by angling a putty knife toward the corner where the trim meets the wall and tapping the putty knife behind the trim with a hammer. Push back on the handle of the knife to pry the trim forward along the perimeter of the room.

Set a circular saw to a half-inch in depth. Cut into the subfloor roughly 6 inches from either side of the wall where the rotted subfloor is located. If the half-inch blade doesn’t cut through the subfloor boards, change the setting to three-fourths inch and repeat the cuts.

Cut the floorboards again, directly against the base of the wall. Use a hammer to pry the nails up from the floorboards and pull up the loose pieces of flooring next to the wall. Tap the sections of the floorboard directly beneath the wall out into the open space created alongside the wall.

Use a putty knife to scrape out any rotted sections of the floorboards beneath the wall that remain once the main sections of the boards have been removed. Shine a light beneath the wall and scrape out any rot in the joists as well. If you find rot in joists, use a screwdriver and hammer to chisel out a rectangular section of the joist and measure the section once you have chiseled it.

Cut down wood pieces to the sizes of the sections of wood removed from the joists. Cover the bottom and side edges of the wood pieces and press them down into place in the joists. Set bricks or weights on top of the new wood sections to hold them while the adhesive dries for the amount of time the manufacturer recommends.

Trim down wood floorboards to the length of the area from which you removed the original rotted floorboards, incorporating the area under the wall and the empty space on each side of the wall in the measurement. Cut these boards in half.

Slide the floorboards back into the floor from either side of the wall, placing the end of each piece under the wall, then lowering the board down onto the floor. Nail the floorboards into place by driving nails through the boards and into the joists.