How to Fix Sagging Plywood Subfloors


Sagging plywood subfloors are often caused by water damage due to leaking roofs and plumbing leaks. Sagging subfloors can be very dangerous and need to be replaced right away. Often only a small section will need to be replaced, such as a section of bathroom or kitchen subfloor.

Things You'll Need

  • Circular saw
  • Plywood
  • Nails
  • Hammer
  • Chisel
  • Razor knife
  • Safety glasses
  • Level
  • Leveling compound
  • Pull up the flooring over the plywood subfloor. If the flooring is tile, use the chisel and hammer to break it up and remove it. If the flooring is laminate or carpet, use the razor knife to cut out the section and use the claw on the hammer to pull it up. If you're dealing with hardwood flooring, use either the chisel and hammer or the circular saw to cut it out.

  • Cut out the sagging subfloor using the circular saw. Determine where the floor joints are located and cut the subfloor all the way to the joints. Leave at least half of the floor joint exposed. Be careful not to cut any wiring or piping under the subfloor.

  • Measure the hole in the floor and cut the new piece of plywood to these dimensions. Make sure all of the edges of the plywood are clean and free of debris.

  • Place the newly cut plywood in the hole. Make sure there is enough room for the edges of the plywood to rest on the floor joints and nail the plywood into place. Use enough nails to ensure the plywood does not slip out of place.

  • Place a level over the newly installed subfloor to ensure there is no slope. If the subfloor is not level, try sanding it down to make sure it is even with the rest of the subfloor and check with the level again. If the subfloor is still not level, you will need to apply the leveling compound.

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  • "The Complete Guide to Contracting Your Home"; Dave McGuerty, Kent Lester; 1997
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