Subfloors are a structural part of the house that needs replacing when damaged. There are telltale signs of subfloor damage that indicate damages and hint at a coming replacement. However, even though replacing the subfloor is not that complicated, replacing the subfloor under a wall is a different story. And if the wall in question is a load-bearing wall, then that is definitely not a beginner DIYer’s job.

However, if the subfloor under a wall gets damaged and needs replacement, you can do it yourself as long as it is not a load-bearing wall. Still, you need a thorough understanding of the flooring layers and how the wall is placed on top of the floor to replace subfloor under a wall. This article will discuss the basic principles of how the walls and floors are structured and give a step-by-step guide on how to replace the subfloor under a wall. So let’s get into it.

Tools and Materials Needed to Replace Subfloor Under a Wall

How to Replace Subfloor Under a Wall

Step 1: Assess the damaged floor

First, you need to assess and determine the subfloor’s condition if you haven’t already. Next, remove the floor covering on both sides of the wall to expose the subfloor for assessment. You should also inspect and find the reason behind the damaged subfloor. For example, you should take proper care of water damage from a leaky pipe before installing a new subfloor. Also, mark the spread of the damage to help you gauge how much baseboard and drywall you need to remove in the next step.

Step 2: Remove the baseboard and drywall

Remove the baseboard and any quarter-round trim in the marked area using a flat pry bar. Set the baseboard pieces aside for reattaching them in the end. Use the handsaw to cut away a section of the drywall. Cut out an area large enough so you can access the damage comfortably. You might need to cut out from both sides of the wall if you have insulation.

At this stage, you should be able to see the wall studs and floor plates. Assess them for damage and decide whether they need replacement. Either way, you need to remove the floor plates to remove the floorboards in the next step. Unscrew the wall studs and use a rubber mallet to push them out further. Also, cut off the ends of any rotten wall studs. You can also insert the oscillating multi-tool with a metal-cutting blade attachment under the wall bottom plate to cut the nails that run downward.

Step 3: Remove floor covering

Remove the floor above the damaged subfloor. You should remove an inch or two over the marked perimeter to access the lower layers easily. This should be easy if you have click-and-lock flooring planks parallel to the wall. You can also pry off engineered hardwood and solid hardwood planks with minimal damage. But if you have tile flooring, you need to break them and pry off the mortar that holds them to access the subfloor.

Step 4: Remove the underlayment

Underlayment is an optional part of the flooring layer. However, some flooring materials, such as laminate or luxury vinyl planks, often have underlayment. So, remove the foam or felt underlayment using a utility knife from the section where the floor coverings have been removed. If it’s an underlayment board, you can use your circular saw also in this step.

Step 5: Remove the subfloor under the wall

Set the circular saw to the proper depth, so it cuts only the subfloor without touching the joists below. You should get as close to an inch off the wall using the circular saw. Then, use a hand saw to make two more cuts along the cut-out side until you reach the bottom plate of the wall.

If your subfloor is heavily damaged and rotted, you should be able to pull them out at this stage. If the subfloor does not come off, attach an auger bit to the drill and drill to a depth of 3 and a half inches underneath the wall bottom plate on both sides of the area. The auger bit effectively cut away at the wood like a saw. If you can reach the point where the joist meets the subfloor, you should be able to pull out the section. If the joist is on the other side of the wall, proceed to the next step.

Step 6: Remove the subfloor from the other side of the wall (if needed)

You cannot pull out the subfloor if it continues beyond the wall. So, you must repeat steps one through five on the other side of the floor and cut out the subfloor where the sheet ends. It should free up the subfloor, and you can pull it out.

Step 7: Finish up

After successfully removing the subfloor, it’s time to put it all back together again. If the joist needs repair, follow through before installing new subfloor panels. Next, restore the floor plate and replace any damaged wall studs. Lastly, reinstall underlayment, insulation, and drywall. Finish off the job by painting the wall and replacing the floor covering.

Can You Replace Just a Part of a Subfloor?

Before replacing the subfloor, you first need to inspect its condition. Often, these inspections reveal that the damage is contained in particular subfloor spots. For example, if you have water leaks, the adjacent subflooring might only be subjected to damage. In such a case, you don’t need to replace the entire subfloor but the damaged parts only.

To replace particular areas of the subfloor, you need to make precise cuts through the planks or the plywood, which is pretty straightforward. You also need to replace the floor covering in that area. However, the complication begins when you hit the nails or screws used to fasten wood subfloors which can dull even the best circular saw blade in an instant. So, you must remove the nails connecting the subfloor to the joists before cutting off the damaged parts. Then, you will need to re-fasten the subfloor to the joist once you have successfully replaced the damaged subfloors.

Do Walls Go on Top of a Subfloor?

Although it is pretty intuitive, some people might be confused about the architecture of the floors and the walls and how they are connected. First, the answer to the question is yes, walls do go on top of a subfloor. Any other way would be impossible or at least difficult with no added benefits.

Before going into how to replace subfloor under a wall, let’s go through the layers of your floor (yes, there are more layers in your floor other than the one you see) and how the walls sit on top.

• Joist: Joists are a horizontal structural part of the flooring that spans an open space, typically between beams, which transfer the load to vertical structural components of the house. They carry the weight of everything inside a room, including walls, furniture, appliances, and even people.
• Subfloor: The subfloor is the bottom-most layer of flooring that rests on the joist and supports all the other layers. It is a structural part of the floor. Subfloors are typically very thick, with the thickness ranging from 19/32 inch to 1 1/8 inch. It is usually made of plywood, particleboard, or OSB. The slab is considered the subfloor for the concrete slab floor.
• Underlayment: Underlayment is the flooring layer that lies immediately under the visible flooring. It is usually ¼ or ½ inch thick and can be made of many different materials that depend on the floor covering. You might not always find this flooring layer as many materials do not require it. The primary function of underlayment is to provide a smooth surface for installing the floor covering.
• Floor covering: Floor covering or the finished floor is the part of the flooring layers you can see or walk on. There are many different flooring options for you to choose from for your home. The most popular flooring options are ceramic tile, hardwood, engineered wood, laminate, luxury vinyl, bamboo, cork, and carpets.
• Bottom wall plate: As the name suggests, it is the bottom-most part of the wall. Wall plates are nailed into the subfloor. If joists are running below the wall (which is the standard), the nails connecting the wall plate to the subfloor can even extend into the joists. The wall studs are nailed vertically to the bottom wall plate. The underlayment and the floor covering are skipped in these parts of the floor. All the other flooring layers are nailed to the bottom wall plate.

Can you Replace Subfloor under a Wall?

Yes, you can replace subfloor under a wall, but it is difficult as it is trapped under the wall. It can be done, but you need patience and time if you don’t want to risk damaging the wall. Instead, remove part of the subfloor if you want to keep the wall. If you want to remove the entire subfloor under a wall, you will have two options. You can either remove the wall entirely and rebuild it after the replacement or go section by section and remove and replace a single part of the subfloor at a time. A safe width to remove at one go is 14 inches, representing the span between the adjacent joists.

Another factor to take into consideration is whether the wall is load-bearing. If it is a load-bearing wall, you will need to shore it up so it doesn’t collapse while replacing the subfloor. You may also need to create a brace underneath the joists for extra support when removing and replacing the subfloor under a load-bearing wall. Since it is somewhat tedious, we recommend contacting a professional if the subfloor under a load-bearing wall is damaged. Also, the subfloor underneath a load-bearing wall is under consistent pressure. So, if you suspect it is damaged, you should check it out quickly to avoid further damage to your home’s structure.

Although replacing a subfloor under a wall is not a simple process, it can be done if you have the expertise and follow the step-by-step process precisely. But, of course, having the right tools and materials handy is also crucial. And if you are unsure, do not hesitate to contact an expert before taking on a major project such as replacing subfloor under a wall.