Sometimes a little patch is all you need—but this project is no small job
If your floor looks or sounds a little wonky, there could be trouble lurking underneath. You might need to replace your subfloor. This base layer of particle board or plywood supports your chosen floor material (be it high-end hardwood or cost-effective vinyl). It’s not always a straightforward task, but this guide can help. Here’s how to replace subflooring—whether you’re patching a small area or ripping out the entire floor.
If you’ve recently had severe water damage that’s warped your floor, you probably need to replace the subfloor. It’s not always this obvious, so keep an eye out for the following signs:
Unusually squeaky floorboards
Cupped floorboards
Sinking sections of flooring
Cracked or popping tiles
Loose spots of flooring
A wobbly toilet
Water stains on the ceiling below the floor
Moldy or musty spells coming from the floor
Water damage can cause serious problems for flooring, such as warping, staining, and mold growth. If you suspect water damage is an issue, a flooring pro can diagnose the cause, make necessary repairs, and restore the integrity of your floor.
Replacing subflooring is a relatively complicated task that requires precise measurements. You’ll need to make sure all of the parts of your floor are structurally sound. That said, you don't always need to replace the entire subfloor. If only a portion is damaged, you can patch it. These steps will show you how.
To understand how to replace a subfloor, you need to familiarize yourself with the anatomy of a floor. Your floor has a few key parts, which you’ll need to inspect, reinforce, replace, or remove to repair the subfloor:
Floor Joists: Joists are horizontal pieces of wood that support the flooring. They’re like the skeleton of the floor.
Subfloor: The subfloor rests on the joists and acts as the base of your flooring.
Underlayment: Some floors have a layer of material that covers the subfloor, which aids in insulation, sound absorption, and smoothing out the subfloor.
Floor Covering: Your floor covering is the top of your floor—think: hardwood, laminate, tile, or linoleum flooring. Whatever the material, your floor covering rests on top of the subfloor or underlayment.
Before you can replace your subfloor, you need to understand the extent of the damage. If the floor joists are compromised, you could have a much larger problem. If possible, check the underside of the flooring (from a crawl space or basement) and look for visual signs of damage along the joists and subfloor. If you have carpet or flooring that’s pulling up at the edges, look underneath to locate the subfloor damage.
If you cannot access your joists, it’s important to call a local flooring company to assess whether or not the floor is structurally sound.
Electrical wires and pipes could be hiding near your subfloor. To be safe, before you start pulling up your floor, make sure you turn off any electrical circuits or water lines that run to the area. If you don’t have intermediary water shut-offs, you’ll need to shut off the main line.
Carefully remove the floor covering over the section of the subfloor you plan to replace. It’s a good idea to give yourself a little leeway by extending the area by a few inches beyond the damage. Don’t forget to remove and set aside any floor transition strips that are in the way, too.
How you remove the flooring depends on the type. You can typically peel off vinyl tiles or pry off wood or engineered wood floor boards (prepare to budget for the cost of refinishing your hardwood floors if they sustain damage in the process). If you have tile or ceramic flooring, you’ll likely need to break the tile and chip away the grout to remove it.
If your floor has an underlayment, remove it too. You can cut away foam or felt underlayment using a knife. If the underlayment is made from a thin, plywood board, it’s more difficult. You will need to use a circular saw—but beware of pipes, wires, and joists beneath it. Always follow safety precautions when using equipment like a saw and wear the proper safety gear.
Once you’re down to the subfloor, mark the area you want to remove, so you know where to cut. Typically, you’ll want to remove the subfloor from the center of one joist to the center of another joist. Choose the joists closest to the damage; you can find them using a stud finder.
Removing the subfloor involves a few simple steps. Most of the time, contractors use a circular saw, though the method may vary depending on the material:
Set a circular saw to the proper depth so you don’t accidentally damage a joist, pipes, or wiring.
Use your saw to cut along your markings and cut out the damaged piece of subfloor.
Use a screwdriver to remove any screws you find as you’re cutting.
Use a pry bar to pull up the damaged floor.
If there are any hard-to-reach areas as you cut, you might find it easier to use a reciprocating saw. Make sure to use a vacuum cleaner to clear the debris after you remove the subfloor.
Once you’re down to the subfloor, you can take a closer look at the joists. If they’re severely damaged, you may have to replace them entirely. Most of the time, you can reinforce a damaged joist by attaching an additional support joist using construction adhesive.
If your floor joists are structurally sound, you can install the new subfloor. If you’re covering a large area, you’ll want to stagger joints between sheets so your flooring has a bricklaying pattern. Make sure the ends of the plywood—where the tongues and grooves connect—are centered on a joist.
Glue and screw the plywood into the joists. The construction glue will help prevent squeaky floors and reinforce the screws.
Now that you have a new subfloor or subfloor patch, it’s time to install the rest of your floor structure. If your subfloor was damaged by moisture, this might be the time to start waterproofing—whether you add a waterproof underlayment or install new epoxy floors. In the same breath, if your old floor wasn’t damaged during the removal, you can reuse the same material (this is common with hardwood or engineered wood planks).
Subfloors are fairly sturdy, so there are only a few reasons you’d really need to replace them. The main culprit is usually water damage in your home—be it from a flood, a leaking pipe, or a faulty seal around an area regularly exposed to moisture. For this reason, you’ll typically find damaged subflooring around windows, doors, bathtubs, showers, and toilets or in basements, bathrooms, and kitchens. Some less common reasons include:
Pest infestations
Foundation settlement
Earthquakes
Fires
Subfloor replacement is a tricky DIY, but these tips can help make the job go as smoothly as brand-new hardwood beneath your feet.
Say goodbye to creaky floors. Rather than traditional plywood panels, opt for tongue-and-groove subflooring. This type of subfloor has grooves that slide into place and create an ultra-sturdy connection—especially when glued. They’re typically made from oriented strand board (OSB) or CDX.
Wood is subject to thermal expansion, even if it’s plywood or particleboard. When you install your subfloor, leave about 1/8-inch of space between each piece of plywood to account for expanding and contracting.
Sanding down the edges of your plywood panels will help keep them flush and prevent them from sticking up. This will smooth out the look of your floor once you reinstall the floor covering.
If you need to replace all of the subfloor in a room, you’ll need to access the section behind the wall. This requires you to remove part of the wall. You’ll need to pull off the baseboards and cut away sections of drywall that extend over the subfloor. In this case, you may want to call flooring contractor.
Since wood does contract and expand depending on the temperature and moisture level, the replacement subfloor needs to acclimate to the specific temperature and moisture levels in your room. Take the plywood out of storage, and place it in the room where you plan to install it. Let it sit for a few days before starting your project.
If you have access from the basement, it may seem easier to replace your subfloor from underneath, which allows you to keep your floor covering in place. Just don’t do it—always remove the subfloor from the top to ensure it’s installed correctly and securely.
The cost to replace subflooring is typically $450 to $3,000 if you hire a pro. Costs will slant towards the high end if you need significant repairs because of structural damage or mold removal. In some cases, floor joist replacement could cost $5,000 to $20,000.
If you plan to replace your floors, you may also need to replace the subfloor. Make sure to factor this into your total flooring installation costs. For the average homeowner, a new floor costs $1,500 to $4,500.
Some subfloor repairs are relatively straightforward while others are more complex—but none of them are suitable for beginners. This is a complicated process that involves precise measurements, construction knowledge, and the ability to diagnose and fix flooring issues.
Though materials generally cost $3 to $10 per square foot, a DIY job isn’t affordable if you make a costly mistake. It’s best to call a flooring company near you unless you really, really know what you’re doing—especially if you’re dealing with damaged joists or severe water damage.
A good subfloor can last 30 years or even longer, depending on the material. OSB should last a bit longer than plywood. However, OSB isn’t the best option for heavy flooring types like ceramic tile or stone. It’s also worth noting that regular moisture exposure will drastically reduce any subfloor's life span.
The most popular subfloor materials are OSB and CDX because they’re relatively inexpensive and can withstand exposure. In general, you’ll want to choose a tongue-and-groove style because it makes for a sturdier floor that isn’t prone to squeaking.
You might also have a concrete subfloor. This is common in basements or homes built with slab-on-grade foundations. If that’s the case, you can use a concrete patch kit to fix minor damage.
Dry rot or severe water damage may warrant a replacement, but you don’t always need to replace damaged subflooring. If your subfloor has warped because it was installed incorrectly, you can sometimes shim the panels (in other words, add a thin, wedge-shaped piece of wood to level the surface). If your subfloor bows upward, you may be able to sand it down at the joist so it’s level, depending on the extent of the damage.
Most of the time, you’ll want to use screws on your subfloor rather than nails. Nails can actually weaken plywood, whereas screws can easily penetrate without damage. They also form a more secure connection because of their shape, preventing squeaky floors and tightly holding the subfloor in place. That said, some contractors do prefer nails depending on the type of floor covering because they allow for more flexibility.
