The Correct Ways to Replace the Rotted Subfloor in a Bathroom

Rotted Wood

• The most effective method of repairing a rotted subfloor is to remove all rotted or wet wood and to allow the area beneath the floor to dry completely before recovering it. If the source of the leak is known, often you can remove enough flooring to reveal about one foot of good subfloor all the way around the rotted area, but ideally you should pull up all of the flooring in the room to determine whether more than one area has been subjected to moisture. Cut away the subfloor around the rotted area and into the good wood beyond it. Be careful to avoid damaging the joists beneath as you work. It is critical to remove all rotted subfloor material.

Support

• The floor joists are critical to providing proper support to your new floor, so after removing the rotted material, use a stud finder to locate the next available joist beyond the point where the rotted subfloor ends on all sides of the rotted area. Cut out the subfloor up to these points so that half of the joist is revealed. If the joists are wet, they need time to dry before covering with a new subfloor. Place a dehumidifier in the room or apply heat to speed the drying process. When they are dry, cut a 2-by-4-inch board to fit along the side of each revealed joist, and fasten these to the side of the joists so they are flush with the tops of the joist. These new 2-by-4-inch boards will provide a solid, supportive base to fasten the new subfloor to, particularly if the joists have been subject to decay or moisture.

New Subfloor

• Subfloors are usually made up of two layers. The first is 1/2- or 3/4-inch plywood or oriented strand board which provides a solid surface for traffic. The second layer is an underlayment, such as Luan plywood, which provides a clean, smooth surface to lay your flooring over. Make sure the new subfloor material is the same type and thickness as the old material. Replacing with a different material or one slightly thinner or thicker may cause problems when you lay your new flooring down later.

Finishing

• The finished surface of the new subfloor should be smooth and lay flush with the old subfloor material. If you’ve removed only a portion of flooring, cut the patch piece of plywood to fit the opening and fasten it to the 2-by-4 boards that you fastened to the joists using drywall screws. Space the screws about 10 to 12 inches apart along the length of the joist. Do the same with your underlayment, but fasten this to the plywood using nails that are spaced 6 to 8 inches apart. This closer spacing prevents the plywood from buckling due to temperature or moisture fluctuations. When the new material is secured, you’ll have cracks where the new wood and the old wood meet. You may also have depressions caused by hammering the nails into place. Use wood putty or a floor leveler to fill these and to make a smooth, even surface for your new flooring.