How to Replace a Water-Damaged Subfloor

Once the wooden floor of your home or building becomes damaged by water, it is imperative that you remove the water-damaged area as soon as possible to prevent the onset of mold and fungus. This not only includes the subfloor but also any adjacent areas such as the floor joists or house frame. In most cases, removing the finish flooring will also be necessary. In the following article you will find some helpful guidelines explaining how to deal with the problem.

Difficulty: Challenging

Instructions

Things You'll Need:

• Old work clothes
• Heavy leather gloves
• Dust mask and safety goggles
• Flat pry bar
• Cat's paw pry bar
• 4-foot crowbar
• 20-ounce straight claw framing hammer
• Sawhorses
• Safety glasses
• Circular saw
• Chalk line
• Tape measure
• Reciprocal saw
• Old wood chisel
• Wood sealer or creosote
• Galvanized flooring nails (#6 or #8)
• Galvanized framing nails (#16)
• Exterior-grade plywood of matching thickness

How to Replace a Water Damaged Subfloor

1. Tear away the finish floor to get to the subfloor. Unfortunately, this step is unavoidable. Save whatever pieces you can, but it is highly likely that if the subfloor is water damaged, then the main floor will also be in bad shape. Use pry bars and flat bars to pull loose the old boards or whatever floor covering you might have.

2. Tear away the water-logged subfloor. In many cases this task will proceed quite quickly due to the deteriorated condition of the plywood or particle board that is usually used for a subfloor.

3. Tear out the good part of any sheet of plywood or particle board that has been partially damaged by the water. This will take more patience and much use of the flat pry bar and the cat's paw, which is a pry tool specifically designed for pulling up nails. By taking out the whole sheet, instead of just the damaged area, the reinstallation becomes much easier.

4. Cut out partial pieces of the flooring with a circular saw that is fitted with a carbon-tipped blade. This may be necessary if the sheet of plywood continues underneath a wall. Then you will need to cut the plywood along the center of a joist. Use safety glasses or a clear face mask when you do this. A better alternative is to make your cut right next to the existing floor joist, where there are no nails. Then you can add a 2-by-4 to the side of the joist. This way you will avoid running your saw blade through any metal nails, which is a very dangerous procedure and should be avoided if at all possible.

5. Replace any water-damaged floor joists. Sometimes the bad part of the joist can be cut away and then splices can be applied to both sides. You can do the cutting with a reciprocal saw. Other times the whole joists may have to be replaced.

6. Pull out all loose nails from the exposed floor joists and prepare to add new plywood. This may require additional blocking with 2-by-4's. Nail any 2-by-4 with galvanized framing nails (#12 or #16 ) and you can paint any potential trouble spots with a sealer or creosote.

7. Cut and fit the plywood into place. You can replace particle board with plywood if the thickness is the same. Make sure the plywood is the same thickness as the old subfloor and use 2-by-4 blocking to shore up the old frame, if necessary. If you are replacing tongue-and-groove plywood subflooring, just cut out any exposed tongues with a wood chisel and cut the new plywood to fit snugly. Only if the damaged area is extensive should you concern yourself with using replacement tongue-and-groove plywood. Use #6 or #8 galvanized floor nails to secure the plywood to the joists.

Tips & Warnings

• Pull all nails from the old plywood as soon as it is removed.
• Make sure all water-damaged areas are removed, even if they are located under an existing wall. Be sure that you repair the problem that caused the water damage in the first place. Leaky roofs and bad plumbing are frequent causes of water damage.

[dhl00]

on 9/23/2009 I have a very slow leak in a pipe in my crawl space under my kitchen sink area. The vinyl covered kitchen floor is sagging in this area and the support feels soft. Can I use 3/4" pressure treated plywood to replace either the original first layer of subfloor and/or the layer on top of that. I probably will recover the floor with vinyl.

dave in doo