How to Replace a Subfloor Under a Wall

How to Replace a Subfloor Under a Wall

1. Remove the Baseboard

   Using the flat pry bar, gently remove the baseboard and any quarter-round trim near where you wish to remove the subfloor. Set these pieces aside.

2. Remove Sections of Drywall

   The next step is to remove sections of drywall. It may extend over the floor covering—if this is the case, cut away a section to the required width and about 1-foot high. Place any trash out of the way in a heavy-duty trash bag.

3. Remove the Floor Covering

   Remove the floor covering directly above the subfloor that you want to remove. Also, remove a few more inches beyond to give yourself room to work. Some floor coverings will lift off easily, while others will require cutting.

   You should be able to lift any laminate flooring and luxury vinyl plank flooring installed parallel to the wall. Self-adhesive vinyl tiles will peel off and sheet vinyl can be pulled back. Ceramic and porcelain tile will need to be broken, plus the thinset mortar that holds it down should be chipped away. Solid hardwood and engineered wood flooring installed parallel to the wall can be pried off, though some boards may end up damaged.

4. Remove Any Underlayment

   Some floors have a thin underlayment between the subfloor and the floor covering. For laminate flooring with a foam or felt underlayment, cut away a section with the utility knife. For 1/4-inch luan underlayment board, set the circular saw at the correct depth to cut only into the luan but not any of the materials beneath it.

5. Cut Away the Nails

   Attach the metal-cutting blade to the oscillating multi-tool. While wearing eye and hearing protection, turn on the tool and insert the blade under the wall bottom plate. Cut away all nails that run downward from the bottom wall plate.

   Tip

   A nail puller tool (often called a cat’s paw) can be used to dig into the wood of the plate or subfloor around the nail head so it can be pulled out rather than cut. This will remove the nail completely, so the subfloor will not get hung up on any uncut portions.

6. Cut Away the Subfloor

   Set the circular saw to the proper depth to cut only the subfloor but none of the materials below the subfloor. Keep in mind that the circular saw cannot cut flush with the wall, so just cut as close as you can get to it—most saws will let you cut as close as an inch or two. Continue with two more cuts with the hand saw along the side of the cut-out square until you reach the wall’s bottom plate.

7. Remove the Subfloor From Under the Wall

   If your subfloor is heavily rotted, you may be able to pull back on the remaining section of the subfloor and remove it by hand. If not, attach a 3/4-inch auger bit to the drill and drill to a depth of 3 1/2 inches underneath the wall bottom plate on both sides of the rotted area. The auger bit effectively acts as a saw to cut away at the wood. If the edge of the subfloor rests on the joist, the section of the subfloor should pull out. If not, proceed to the next step.

8. Remove Subfloor From the Other Side (If Necessary)

   If the subfloor is a continuous sheet that extends beyond the wall, you will not be able to pull out the section that you are working on. Repeat all of the previous steps on the other side of the wall to free up the subfloor so that you can remove it.

When to Call a Professional

If you need to replace the entire subfloor under an exterior wall or a load-bearing wall, it may be time to hire a professional. Special considerations must be made to prevent the walls from sagging or hanging down while the subfloor is not in place to support them. Smaller sections of the subfloor—up to about 14 inches wide between joists—can be cut out and replaced without needing extra support.