How to Replace Rotten Subflooring

When a subfloor gets wet or is concealing moisture, it will feel spongy. The floor can be dangerous and unhealthy. It will rot to the point of giving way under weight, and it could be hiding mold that can make you sick. Replacing the subfloor is not that difficult, but when you're done you will still need to install new finish flooring on top. Before you do, though, make sure you know what caused the rot in the first place, or you will be doing the entire job again very soon.

Things You'll Need

• Saw
• Measuring tape
• Hammer
• Chisel
• Wood screws
• Screwdriver/drill
• 3/4-inch plywood
• Utility knife

Instructions

1. View damage from the basement or crawlspace if possible. There are two reasons for starting under the damage. One is to see if there are any wires or plumbing that you don't want to cut through with your saw from the top, and the other is to see how much damage there is. If you have carpet or tile in the room above that you can match, you may not have to rip up the entire finish flooring.

2. Take up the finish flooring. Remove either all or part of the flooring to reveal the damaged subfloor. You will want to cut out the flooring at least a foot past the damage into good wood or remove all of it. If you are removing only part of it, you will want the sections to be from the center of one floor joist to the center of another. If you are removing all of the flooring, you will need to chisel out the edges over the floor joist, because you will not be able to get your saw over it, due to the walls.

3. Pull any nails or unscrew any screws that are stuck in the floor joists where you removed the plywood. Clean off the floor joists of any wood splinters, sawdust or anything else that may be on them. At this point, if the joists are wet from the damage, let them dry out before putting new wood on them. You can use fans or heat to speed the process up. Make sure the problem is fixed so your new subfloor does not get any damage.

4. Lay new 4-foot-by-8-foot sheets of 3/4-inch plywood so that the edges rest from center to center of a joist and screw into the joists with wood screws. Screw into the joists between also. If the area you are repairing won't take a full sheet, measure it and cut the plywood to fit. Repeat putting in new boards until the area is completely covered.