How to Make the Floor Sturdier Underneath a Toilet

Shut off the water supply to the toilet at the wall valve then flush the toilet to remove the rest of the water. Remove the bolts that hold the toilet to the floor with an adjustable wrench. Lift the toilet off of its wax ring and set it aside.

Remove the old flange if it needs to be replaced. Scrape away any of the old wax seal that remains. Drill holes side by side around the ABS coupling in the flange then cut all the way around it with a hacksaw. Remove the screws that hold the flange in place with a drill. Cut away the rest of the coupling to the sewer inlet with the hacksaw.

Measure the area of floor around the flange that needs to be replaced and reinforced. Use a carpenter’s square to draw a square on the old floor. Make the area large enough so that the floor joists can be used for support.

Use a circular saw to cut around the lines you’ve drawn on the subfloor. Set the saw to the same thickness as the subfloor, which is typically 1/2-inch. Remove the old piece of floor.

Cut pieces of 2-by-4 to frame the inside of the opening and support the replacement floor. Mount the pieces between the floor joists with deck screws. Position them high enough to support the new floor.

Cut a new piece of 3/4-inch plywood to match the size of the opening you made after removing the old floor. Cut a square opening in the center for the flange and sewer inlet.

Drill deck screws through the new piece of subfloor and into the 2-by-4 support struts you just installed. Drill around the perimeter of the new wood until it is secure and won’t shift.

Apply ABS glue to the inside of the sewer inlet and the outside of the new flange then set the flange in place. Replace any carpet or hard flooring then set a new wax ring in place. Reinstall the bolts into the floor then replace the toilet.