How to Repair Rotted Wood Flooring

An old wood floor that's soft and rotting presents the real danger of stepping right through it. It's an especially common problem around toilets, because of the moisture that can buildup there. Fixing the problem right requires complete removal of the rotted floor material down to joists, and cutting it back to the non-rotted part of the floor, then re-supporting it underneath and putting on new underlayment. It's an involved project, and you should be comfortable with your carpentry skills before attempting it. (NOTE: If the rotted floor is on the ground level of a house, with an unfinished basement that gives you open access underneath the floor, you can do much of the work from the basement, and it's a much easier project. This article assumes you're not that lucky, and that you can't access the problem from below.)

Things You'll Need

• Jigsaw with wood-cutting blade
• Circular saw
• Drill with screwdriver bit
• Two 8-foot lengths of 2x4 (more, if the rotted area is more than a few square feet)
• Tape measure
• Pencil
• Level
• One 4x8-foot sheet of 5/8-inch plywood underlayment
• Box of 1-1/2-inch drywall screws
• Box of 3-inch wood screws

Instructions

1. Clear the area of all obstructions. If the rotted area is around a toilet or pedestal sink, remove them. Pull up as much of the rotted wood as you can by hand. Determine which direction the parallel support joists underneath the floor are positioned. If there's not a full hole in the floor at the "soft spot,'' cut one, using your jigsaw, so you can either see the joists through the hole in the floor or reach in and feel them.

2. With your jigsaw, cut from one edge of the hole in the floor and toward the nearest joist, cutting and removing rotted pieces of the floor as you do, until you can look right down at the joist. Cut away enough of the surrounding floor so that you can set the jigsaw blade alongside the joist and begin cutting from that angle, running along the length of the joist in both directions until you're a few inches beyond the rotted area and into solid floor. You should be working exclusively on one side of the joist, the side where the floor is rotted. Be sure not to cut into the joist itself.

3. Work your jigsaw to the other side of the rotted area, finding the first good joist on that side and repeat the process, cutting the floor up to the edge of the joist.

4. With your drill and screwdriver bit, sink 1 1/2 inch screws every six inches into the edge of the floor where you've cut and down through the top of the joist, to secure it tightly. Repeat the process on the second joist at the other edge of the hole.

5. Use your level and pencil to draw two straight lines on the floor between the two joists, at the edges of the hole. Use your jigsaw to cut those lines to the sides of the joists. You should end up with a square hole in the floor that spans between the two joists and has no rotting wood at the edges.

6. Measure the span of one open edge of the hole between the two joists, measuring from one joist to the other and use your circular saw to cut a 2x4 piece at that length. Position the 2x4 lengthwise on its narrow edge under the exposed edge of the hole, wedging the ends of the 2x4 between the two joists. This forms a kind of miniature joist, crossing between the two existing ones. Half the narrow edge of the 2x4 should be tucked under the edge of the floor, with the other half sticking out and forming a narrow "shelf'' in front of it that new subfloor can sit on.

7. With your drill and screwdriver bit, put two 3 inch screws into the ends the 2x4, under the floor level, pointed at an angle so they grip the joists. Then sink a few 1 1/2 inch screws into the edge of the floor and down through the top of the 2x4. Repeat the process on the other exposed edge of the square hole.

8. Measure along one of the original joists to find the length between the two 2x4 that you've affixed at either end and cut another 2x4 piece at that length. Hold the new 2x4 alongside the existing joist, wide side flat against it, with the narrow top of 2x4 lining up with the top of the joist and the two ends wedged within the two 2x4s you affixed earlier.

9. Sink 3 inch screws into the face of the new 2x4 and through the joist behind it, putting screws every six inches or so in two rows along the length of the board. Since the exposed flooring comes right to the edge of the existing joist, the edge of this new 2x4 should form a narrow "shelf'' alongside the joist that the new subfloor can sit on. Repeat the process for the other existing joist. You should now have that narrow "shelf'' on all four sides of the hole.

10. Measure the dimensions of the square hole, not from the 2x4s, but from the inside edges of the exposed floor. Transfer the measurements to your plywood subflooring and, with your circular saw, cut a square piece to fit. Set the piece in the hole so that it rests on the narrow "shelves'' exposed on all four sides. Sink 1 1/2 inch screws every six inches all around the perimeter of the plywood, into the edges of the 2x4s below, to secure the piece. (NOTE: If the square patch is at a lower level than the rest of the floor, cut a second square patch of the same dimensions and screw it directly on top of the first patch to build it up the level of the rest of the floor.) The area is now ready for new underlayment and flooring.

Tips & Warnings

• Always wear eye protection when using a circular saw or jigsaw. Watch out for any electrical or plumbing lines as you're working; never cut with the jigsaw where you can't see. If in the course of taking out the rotted flooring, you discover that the joists themselves are significantly rotted out, then it's a much more serious situation involving the structural integrity of the room, and you should consult a professional contractor.