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How to Repair Water Damage to a Subfloor in a Mobile Home

Elizabeth Sobiski

For any kind of home, water can damage wood subfloors. In older mobile homes, the damage water can do is potentially much worse. This is because particle board used to be the subflooring of choice among mobile home builders.

Plywood is a good replacement for particle board.

Particle board is just what the name implies -- it is particles of wood that are pressed and glued together. When it gets wet, the glue may soften and the particles of wood are no longer bonded. When this happens, the best solution is to replace the damaged area. Plywood or oriented strand board (OSB) are two options to replace the particle board with. Both are stronger than particle board.

  1. Feel for the soft spot in the floor by walking on it if it is not visible. Cut around the soft spot through the floor covering with the utility knife. Peel back the floor covering to see the actual damage to the subfloor. If there seems to be more damage, cut and peel more of the floor covering away.

  2. Use the circular saw to cut out the damaged area. Set the depth guide for the saw blade to the thickness of the subfloor. This may be anywhere from 1/2 inch to 3/4 inch. Pry the damaged section of floor out with the prybar, taking care not to damage the joists under the floor.

  3. Locate the joists on either side of the hole in the floor. You need to enlarge the hole to reach and slightly expose those joists, as they give you something to attach the new subfloor to. Measure the hole and cut a piece of plywood or OSB to the same dimensions to create a patch. Use plywood or OSB that is the same thickness as the particle board you removed.

  4. Set the patch into place and attach to the joists underneath with screws. Use one screw in each corner and other screws spaced every 6 to 8 inches around the perimeter of the patch. This will hold the patch firmly in place.

  5. Replace the floor covering that you peeled back earlier. Use a construction adhesive that bonds your particular flooring to wood. Take care when replacing the floor covering so that the seams are not noticeable.

  6. Tip

    If the damaged area is large, replace all of the subfloor in the room. This is also an excellent opportunity to replace floor coverings.


    Fix the leak, or other cause, of the water damage before replacing the subfloor. Otherwise the new subfloor will not last as long as it should.

    Use safety glasses while cutting wood.