How To Replace a Subfloor

How to Replace a Subfloor Under a Wall

1. Remove the Baseboard

   Use the flat pry bar to 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

   Remove sections of drywall that 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 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 must be broken, and the thin-set 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

   Remove any thin underlayment between the subfloor and the floor covering. Cut away a section with the utility knife for laminate flooring with foam or felt underlayment. For a 1/4-inch luan (plywood) underlayment board, set the circular saw at the correct depth to cut only into the luan but not any 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 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 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. Remember 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

   Pull back on the remaining section of the subfloor and remove it by hand if your subfloor is heavily rotted. 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)

   Repeat the previous steps on the other side of the wall if the subfloor is a continuous sheet extending beyond the wall. Otherwise, you will not be able to pull out the section that you are working on.

9. Inspect the Joists

   Removing the subfloor allows you to get a better look at the joists. If the joists are damaged, fix them or replace them now. Often, you can reinforce damaged joists with an additional support joist using heavy-duty adhesives..

10. Install New Subfloor

    Install new subflooring by measuring and cutting a new section of the subfloor to fit the space. When using plywood or tongue-and-groove flooring, ensure the joint connection is centered on a joist. Screw and adhere the plywood to the joists. The addition of gluing helps reduce squeaking or creaking sounds.
    

11. Install the Top Flooring

    If it's in good shape, you can reinstall the previous flooring, such as hardwood, engineered wood planks, or carpeting, or replace it entirely. If this is a problem spot, such as one prone to leaks, consider waterproofing.
    

Tips for Replacing Subflooring

• Replace subflooring from above: It may seem easier to remove subflooring from below, say if you are in an unfinished basement and can see the subflooring; however, gravity will be working against you from this perspective. You will have a better view from above and can more easily remove old nails and other materials.
• Tongue-and-groove flooring is more secure: When weighing whether to use traditional plywood sheets or subflooring, choose tongue-and-groove for a stronger, sturdy, more stable connection. Also, use adhesive for an even stronger hold.
• Leave space for expansion and contraction: Wood and particle board are porous and will expand and shrink with heat, humidity, and cool temperatures. Plan for this by leaving 1/8 inch space between sheets as you lay out the subflooring.
• Give the wood time to adjust: Plywood and subflooring materials should have a few days to adjust to the room's temperature and humidity before being laid. The wood may expand or contract during that time.
• Smooth out the edges: Sand down the corners or edges of panels that stick up or out. Ensure the entire floor is level and even.
  
• Be realistic about the scope of work: Often, people underestimate how much work a project will take. Replacing subflooring sounds easy enough, but if it's damaged and extends past a wall, it might require the wall (or a section of it) to come down. Consider calling a contractor if a project seems like a lot for you. In the end, it might be cheaper, quicker, and better if you get a contractor to help.
  

When to Call a Professional

It may be time to hire a professional if you need to replace the entire subfloor under an exterior wall or a load-bearing wall. 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 subfloor sections—up to about 14 inches wide between joists—can be cut out and replaced without needing extra support.