How to Replace a Rotted Subfloor Under a Wall

Water remains one of the biggest enemies of a home’s inner structure. When leaks happen, they threaten any elements made of unfinished wood, such as studs, joists and subfloors. As water seeps into the wood, the moisture leads to rot and mold. Water-damaged subfloors commonly occur in kitchens and bathrooms where plumbed fixtures are more prominent. This damage often extends underneath walls. Remove the flooring and replace rotten subfloors promptly before the damage begins to extend from the flooring into the wall.

Tape measure
Square
Snap chalk line
Circular saw
Pry bar
Reciprocating saw
Hammer
2 1/2-inch cement-coated nails

Instructions

- 1
  Outline a square area in front of the wall around the damage. Make the square so edges that are perpendicular to the floor joists extend at least one inch past the damage and edges that are parallel to the floor joists extend to the center of the first joist beyond the damage. Use a square to ensure 90 degree corners. Snap a blue chalk line to mark the perimeter of the square.
- 2
  Set the blade of a circular saw to cut to a depth equal to the thickness of the subfloor. Cut the subfloor around the blue chalk line and in front of and as close to the wall as possible.
- 3
  Pry up the subfloor with a pry bar to remove the square section.
- 4
  Run the blade of a reciprocal saw between the tops of the joists and the remaining subfloor under the wall to sever the nails.
- 5
  Dig out the remaining subfloor under the wall with a pry bar.
- 6
  Cut subflooring to match the removed section, including the space under the wall. Nail the subflooring to the exposed joists, using 2 1/2-inch cement-coated sinkers. Place nails every six inches along the edges and every 10 inches along the joists that run under the new section of subfloor.

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