Maybe you noticed a soft spot under the carpet. Or maybe your floorboards are squeaking a little louder than usual. Either way, you’re left wondering: “is it time to replace my subfloor?”
Subfloor damage is typically caused by overexposure to moisture. This could be from excessive humidity, a leak in your plumbing or a crack in your home’s exterior. While the thought of replacing it might give you a sinking feeling – literally – knowing when it’s time to replace your subfloor will allow you to head off more serious problems.
What Is a Subfloor?
A subfloor is the solid material beneath your floor covering. It is attached to your home’s floor joists and acts as a base for your finished flooring, such as carpet, hardwood, laminate, tile, etc. Typically, a subfloor is made of plywood or oriented strand board (OSB) panels.
In areas that are below grade, such as a basement, the concrete foundation is often considered the subfloor, though plywood and OSB panels can be installed over concrete using ground-level floor joists called sleepers.
Do I Need a Subfloor?
It depends. Above grade, hardwood, carpet, laminate and other floor coverings need a plywood or OSB panel subfloor, as they cannot be installed directly to floor joists. Below grade, a plywood or OSB subfloor is optional, depending on your choice of flooring. Floating laminate, engineered hardwood, tile and carpet can be installed directly on a concrete subfloor if the proper moisture barriers are in place.
9 Common Signs of Subfloor Damage
1. Your floors are uneven or sunken in parts.
If you notice a soft spot under carpet or wood flooring, it could mean that the panels below have weakened. While replacing the entire subfloor may not be necessary, you will have to replace the damaged pieces to prevent the rot from spreading.
2. Your floorboards squeak – loudly.
Subfloors squeak when the nails connecting them to the joists are pulled loose. As you walk across the floor, the nails move in and out of the wooden joists, causing the awful, familiar sound of creaky floorboards. If you notice squeaking throughout the entire room, this could be a sign that the material has warped.
3. The room smells musty.
The smell of mold or mildew is a surefire sign of water damage, but the tricky part is finding where. If your carpet or wood floor smells musty, you almost certainly are dealing with a water damaged subfloor.
What are the most common causes of subfloor damage?
“By far the most common cause of subfloor damage is moisture. Common sources are plumbing fixtures, especially toilets and tubs-with-showers, but also any areas with sinks or appliances that are likely to leak, including bathrooms, kitchens, and laundry rooms. Other less common causes are fire and impact.”
Kenton Shepard | Director of Green Building, InterNACHI
4. Your floors shift or bounce when you walk on them.
There’s nothing wrong with having a little spring in your step – unless that springy feeling comes from the floor. If your floors begin to feel spongy, springy or bouncy, or if you notice the floorboards around you shifting when you walk on them, it could mean that it’s time to replace the subfloor.
5. Your toilet is rocking or loose.
“A toilet moves because the subfloor has become so decayed that it no longer securely anchors the fasteners that hold it to the floor,” says Shepard. Often, the moisture damage is from a slow leak in your toilet’s pipes. Since it will only worsen with time, it’s important to get it fixed ASAP.
What are some other areas that are prone to subfloor damage?
“Exterior doors that are poorly installed can fail to protect subfloors from rain and snow, and it’s not unusual to find decay in these areas when inspecting crawlspaces and basements. Especially in warmer climates, crawlspaces that experience seasonal flooding can raise relative humidity to a level at which particle board can experience some deterioration.”
Kenton Shepard | Director of Green Building, InterNACHI
6. Your tile flooring has cracked.
Because tile is inflexible, it requires a strong, rigid surface beneath it to prevent it from cracking. If you notice cracks in your tile floor, it may mean the subfloor isn’t firm enough to hold it up and will need replacing. Keep in mind that when installing tile over plywood or OSB, there must be a cement backerboard between the tile and the panels.
7. Your hardwood floor is cupping.
While it could mean your home’s humidity is too high, hardwood floor cupping could also be a sign that water is warping the materials below. But fear not – you can reverse cupping with the help of professional hardwood drying services, as long as the source of moisture has been addressed.
8. Your linoleum floor is bubbling up.
While bubbling linoleum isn’t always a cause for concern, it can be if it’s caused by moisture building up under your flooring. If there are irregularities throughout your linoleum floor, you may need to look a little harder to rule out water damage to your subfloor.
9. Your ceiling is leaking.
To be clear, a leaking ceiling is not your subfloor’s fault. But it may be an indication that your home has a slow leak. Since plywood and OSB tend to absorb moisture, by the time water has leaked through the ceiling, it could mean the materials are completely soaked through. In addition to calling the plumber, you may want to call a flooring professional to check for subfloor damage.
How Long Does a Subfloor Last?
“A subfloor’s lifespan depends mostly on the materials used and the amount of moisture they’re exposed to,” says Shepard. “Adequately protected from moisture, most subfloor materials can be expected to last for the lifespan of the home.”
However, if the subfloor is consistently exposed to moisture, you may need to replace it after 20 to 30 years or sooner. Subfloor damage caused by water can be reversed with the help of professional tools, but it’s important to catch the signs of rot early to prevent it from spreading to the rest of your subflooring materials.
How Much Does It Cost to Replace a Subfloor?
The cost to replace a subfloor can vary based on a number of factors including the quality, type and thickness of your subfloor material, as well as the additional work required (removing and disposing of the old materials, repairing joists or other flooring features, etc.).
On average, replacing an entire subfloor in a 300-square-foot room can cost between $450 – $2,000. Note that this does not account for the cost of replacing the finished flooring.
Average Cost to Replace a Subfloor
(300 sq. ft)
Professional subfloor replacements in kitchens and bathrooms may cost more than standard estimates. This is because the contractors may have to move appliances or fixtures to finish the installation.
When Repairing Damaged Subfloors, Always Find the Source
If you’ve decided it’s time to replace your subfloor, make sure to fix the source of your subfloor damage as well. Without addressing the root cause of the damage, you’ll eventually need to replace your entire subfloor all over again. Be sure to check nearby pipes, exterior vents and appliances for leaks, and have a disposal plan for any water-damaged materials you come across.
While replacing your subfloor may not be an HGTV-worthy project, it’s an important one to protect your home from further damage, and can save you from even more costly repairs down the line. Plus, it might just be the perfect excuse to install that beautiful hardwood flooring you’ve had your eye on.
Stay ahead of more than just subfloor damage with our preventative home maintenance posts:
I love that you talked about how if you find that tiles on the floor have cracked, you should check to see if part of your building needs repair and improvement because tiles are not very easy to crack. I have a friend whose dad passed away and left her a commercial set of buildings in another state. When she went to see the recently she noticed some cracks and stains on the walls, so in my opinion, she should talk to a professional to avoid having to spend even more money in the future.
HI thank you for the article. Recently I moved out of my house due to water damage. My bathroom had to be redone and a large area of wood flooring had to be replaced. The wood floor was cupping at the seams and had to be replaced. We moved back in and I have immediately noticed slight cupping again in some of the original wettest areas. I also noticed slight squeaking and a more soft feeling where the floor was replaced. It is just a less stable floor where it was replaced although it looks lovely. I found out that the subfloor was never replaced. I believe it was just poor organization. But I am unclear about why. Question: the construction did not replace the plywood under the new floor….after all we went through I am very upset but do I have a justified complaint? is this a normal procedure or should plywood floors have been replaced? It would have been inexpensive to change the plywood but now it will cost a lot to redo everything. What should I do? Any advice welcome. ( Also a moisture reader does reflect a higher moisture where the slight cupping is re appearing. Should I just let it go? I really want forget about it but I can’t afford to this again…..thanks
So sorry to hear about your flooring issues. It’s hard to say definitively whether or not the subfloors should have been replaced at the time of installation. Even after exposure to moisture, sometimes subfloors can be dried out using fans and dehumidifiers and do not need replacing. However, if your subfloors sustained heavy water damage and were not dried out properly, this could be what’s causing the continued symptoms. Flooring contractors should do moisture testing before proceeding with new installation to ensure that the flooring materials will not warp in the long run.
Another possibility is that the floors were dried out properly, but the source of the water/moisture exposure has not been fully addressed. If this is the case, you may want to chat with a plumbing professional to identify the source. Finally, get the professional opinion of a different flooring contractor (one that is licensed and bonded) to confirm whether the issue is with continued moisture exposure or your first contractor’s handiwork.
Again, so sorry to hear about your subfloor issues, we hope this is helpful. Thank you for reading, and good luck!
Flooring that has flooded or has sustained any other types of visible water damage can be a sure sign that it s time to replace your floors. Water can ruin all types of flooring if it is continuously exposed to it for an extended period of time, or if it reaches the subflooring.
We are replacing title and carpeted floors with wood. We’ve noticed after removing the old tulles that there are places where the floorboard has some spring in it. Does that mean it needs to be replaced?
Hi I found this to be good and important information. My second bathroom’s flooring is going crazy…. it is totally crooked. By the sink and toilet side it is lower than the other side of the room. Then the hallway outside of the bathroom it dips down again. I think I am going to have to replace the hole flooring in my home.
Hi Jenna, thanks for reading! We’re glad to hear you found this post to be helpful.
Good luck with your upcoming renovations!
my house is 70 years old and my hardwood floors squeak like crazy. Never had water damage in the 53 years that i have owned The house. do you think it’s old age and the it should be replaced.
How long does it take for OSB sub-floor to rot when exposed to water leak from failed shower pan or leaking toilet ?
It’s hard to give an exact time but if it is continuously getting wet osb will decay a lot faster than plywood
My floor subfloor kepts rotting out the only thing I can think of is mostiure but how can I control this problem
We have a 40 year-old 3 story townhouse. The previous owners rented it, did not take good care of it, and I know there were past leaks. This article confirmed what I expected – that we need to replace the subflooring in many places on both above-grade levels.
My question is – if due to financial and logistical constraints, we can only work to fix the flooring on one level at a time – does it matter if we do the top level or the middle level first? (The bottom level is below grade)
I’ve been building homes and remolding for about 25 years and my advice would be start on the lowest level first because there could be structural damage that wouldn’t be noticed until uncovered
Finally! I’ve been looking everywhere for a good list of flooring tips blogs that won’t straight out advertise their services. Thank you for doing the effort of coalescing these. I agree with most of the listed above. I’ve been through on these home problems today and I was so happy to learn these tips. Thank you!
I paid 800 fo subflooring replacement in my upstairs bathroom however the bathroom when some one rakesg a bath it leaks. Contractor said he fixed all of f that