How to Replace a Subfloor
A damaged subfloor is a serious issue, but replacing it doesn’t have to be intimidating for do-it-yourselfers. Learn how to replace a subfloor in this Lowe’s video:
There are two common ways to build a house:
- Slab on grade: A mold is built out of wood. All of the sewer and water lines are laid out within the mold. Reinforcement wire is added, and then the mold is filled with concrete.
- Crawlspace or basement: The house featured in this video has a crawlspace and sits about two feet off the ground on concrete blocks. The floor joists rest on top of the blocks. Plywood is then added to the top of the joists to create the subfloor.
Subflooring materials include particle board, OSB (oriented strand board), untreated plywood or untreated tongue and groove plywood.
Before you begin repair work, determine the cause of any rotting due to moisture. If the damage was caused by a leaky waterline, you will probably find more rot near the kitchen sink or dishwasher. You should also check around the windows and in the attic spaces.
If the moisture is coming from the ground, install a crawlspace fan to increase air flow and reduce the moisture down there. If water is running off the roof to the ground directly next to the foundation, add gutters and downspouts to direct the water away from the house. You can also install a vapor barrier underneath the house; it’s a plastic sheet which blocks moisture from collecting under the subflooring and the floor joists.
You can repair the floor by patching the existing hole with plywood, but getting the new subfloor to match up perfectly with the old subfloor can be difficult, so it may be best to take out the cabinets and completely demo the kitchen floors and start from scratch.
Identify the location of the plumbing and electrical lines. Using a circular saw and a pry bar, carefully remove the old subfloor one section at a time; to be on the safe side, inspect the next section for plumbing and electrical. Remove all the nails from the floor joist. Use a reciprocating saw to clean up the edges of the flooring near the walls. To get rid of the rotten subfloor beneath the hardwood, remove several pieces of the hardwood to expose the rotten wood, then use the existing edge of the hardwood as a guide to clean up the edge.
Determine how many plywood sheets you will need by using a tape measure or laser tool. You want to attach each side of the plywood to the substructure of the house. Add boards in between the floor joists to screw the new subflooring into; use 2×6 pressure treated lumber. Make sure all the floor and joists are level; if they’re not, either shim in pieces of lumber or add boards to level the floor joists.
To prevent the subfloor from squeaking when walked upon, add a bead of glue to each joist so the plywood subfloor doesn’t separate later. Use 2-inch exterior deck screws with a cordless impact driver. It’s important to leave a 1/8-inch gap between each sheet to allow the wood to naturally expand during the seasons. Fit as many full sheets of plywood as possible, then cut the remaining plywood sheets as necessary to fit.
