Repairing Rotted Plywood Bathroom Subfloor

Turn off the water supply to the bathroom and remove any necessary fixtures. If the floor is rotten underneath the fixtures, they must be removed in order to properly fix this issue. You will need the help of at least one person to move these heavy fixtures out of the way.

Pry up the rotten flooring. Use a pry bar for stubborn areas. Most rotten wood will come out easily and can be removed by hand. Keep a garbage bin handy to dispose of the wood as you go.

Dry out the area under the subfloor. Do not install a new subfloor over a wet surface, you will only re-create the problem. Use a hair dryer for small wet spots, and a portable heater for large areas.

Measure out the width and length for the replacement plywood. If the area is uneven, use a hand saw to even out the panels to make the patch seamless. Uncover at least one floor joist to attach the new plywood properly.

Cut the plywood panel to fit, using a circular saw. Do not rush the plywood through the saw; you can burn the edges or create a jagged mess. Feed it through slowly.

Position the plywood properly and nail it into place along the floor joists. Use a hammer and nails or a nail gun if you prefer.