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How to Install a Subfloor in a Bathroom

Billy McCarley

Bathroom subfloors are no different that any other subfloor, with the exception that bathrooms are usually smaller and must be able to withstand the weight of a bathtub. The structural specification won't change with the size of the subfloor.

Staggered Plywood

The amount of time for installation varies with the size of the bathroom, but the jobs shouldn't take any longer than 1 to 3 hours.

  1. Measure the bathroom floor and determine the amount of plywood you will need. For example, a floor that is 10-feet by 10-feet equals 100 square feet. One sheet of plywood is 4-feet wide by 8-feet long, which equals 32 square feet. Divide 100 square feet by 32 square feet. Based on this calculation, you need 3.125 sheets of plywood for the floor.

  2. Apply construction adhesive onto the floor joists directly underneath the first sheet of plywood. The construction adhesive will add an extra layer of strength and keep the floor from squeaking later on.

  3. Lay the first sheet of plywood perpendicular to the floor joist. Work from left to right and begin in the back corner. Fasten the plywood with 8 penny nails that are space 16 inches apart.

  4. Apply more adhesive under the next sheet of plywood and lay it ahead of the previous piece, lengthwise. Butt the joints together and attach with 8 penny nails.

  5. Stagger the joints in the plywood. Staggering the joints will add strength to the entire floor. See the attached diagram as a reference.

  6. Warning

    Always be careful when using any power tools. Wear safety glasses.