Flooring, Water Damage

8 Signs You Should Replace Subfloor & Costs (Water Damage Included)

Nailing Subfloor Lg

Your former immaculately even floor has started developing soft spots. Some parts make creaky noise, and you think something is amiss with the subfloor. But is it time to replace the surface beneath, or are you misjudging things? 

There are many signs to indicate you should replace or repair your home’s subfloor. If you notice squeaks in the floor, weak spots, cracked tiles, cupping floorboards, musty smells, or loose toilets, it’s time to evaluate and see if you need to fix your subfloor.

You would not easily know what happens beneath the floor surface. Sometimes, you might even ignore the common indicators of subfloor damage as they may not seem too telling.

We’ll take you through the key telltale signs of a problematic subfloor and everything about replacing it. 

What Exactly is a Subfloor in a House?

A subfloor is a surface laid below the visible floor area. It is usually fir, oriented strand board (OSB) or plywood, among other materials. It provides a platform for laying the outer flooring material visible from above, such as tile, hardwood, or laminate. 

OSB is a material made by combining glue and small strands of wood. It is common subfloor material primarily due to its ease of laying and lower cost than plywood. It is also relatively cheaper than plywood or other common subfloor material. Hence, most modern houses will feature an OSB subfloor. 

What people consider a subfloor varies depending on the part of the house. In some parts of the house, like the basement, the concrete flooring may be regarded as the subfloor surface. Often, there is no upper layer to cover the concrete surface. However, it is still considered a subfloor. 

In some instances, the floor is concrete covered by another layer of material. You will nonetheless be required to lay sleepers before installing the top floor material of choice. 

A subfloor should ideally last as long as the house. Hence, frequent subfloor repairs are not commonplace. However, the subfloor may start showing signs of defects in some cases, and it might be time to replace it. 

Most subflooring problems will occur 20 to 30 years after installing the surface. However, depending on the quality of the installation, the issues may crop up earlier. Hence, you should tell when it’s the ideal time to replace the surface. 

Subfloor replacement involves first removing the entire top floor area. Hence, you must be sure that your subfloor area has a problem. Otherwise, you will incur unnecessary costs if you misdiagnose the situation. 

Also, if you are unaware of how to do the replacement, you could do a poor job. Thus, the subfloor will become problematic after some while, and you may have to replace it once again. 

We’ll list down some critical things you need to know before replacing the subfloor. First, let’s look at signs when to replace your subfloor. 

Signs That Your Home’s Subfloor is Damaged

Subflooring replacement generally occurs when the material is damaged, making it unsafe to walk on. However, subfloor unevenness could signify a more significant structural problem in the foundation or floor joists. Many of these conditions overlap, and you may experience several of these conditions at once.

1. Loud Squeaks

The squeaking of the flooring material is common and often happens, albeit unnoticeably. When your floor starts making loud audible squeaks, it usually means the wood is rubbing against a nail, causing the squeak. If you can isolate the location of the squeak, you might fix it with skims or wood screws. 

What causes the loud squeaks is the looseness of the materials in the subfloor. It could be that the OSB or any other subflooring component is loosely attached. Thus, the subfloor material will rub against a nail that joins it to the joists producing the sound. The creaking will be common with subfloor material that has started warping. 

OSB is not as strong as plywood and will flex. As a result, the nails joining them to the joists will loosen, creating squeaky sounds as you step on the floor.

You can often fix a squeaky floor without replacing the subfloor.

2. Weak Subfloor

The subfloor should be even and not have any dips or weak areas. If your subfloor is soft underfoot when walking, or you notice weakness in the subfloor, something is likely wrong with the subfloor installation or the floor structure. Here are some causes of a weak or uneven subfloor:

  1. the subfloor has water damage from a water leak or wet crawl space
  2. the floor joists or trusses are spaced more than 16 inches apart
  3. the edge of the subfloor does not rest over a floor joist
  4. the floor joists or trusses are uneven, the subfloor will be uneven as well and can indicate a stuctural problem

Often, a weak subfloor indicates moisture damage on the underside of the surface, which can occur from a plumbing leak or a wet crawl space. If you have a crawl space moisture problem, your subfloor (and floor joists) can dry rot without you knowing.

If you have a chronic moisture problem, you may need to install a water drainage system, like a french drain, or you may need to encapsulate the crawl space.

During the 1980s and 1990s, builders experimented with floor joist spans wider than 16 inches on center (o.c.) to see how far out they could go without compromising structural integrity. Today, many houses still have floor joists spans of 24 inches o.c. or wider.

When floors joists span wider than 16 inches o.c., the subfloor will flex underfoot unless the builder uses diagonal 1-inch thick floorboards. Plywood and OSB especially need floor joists of 16 inches o.c. to minimize deflection.

However, it could also be due to a poor job laying the subfloor. The rule of thumb during installation is that the subflooring’s ends must meet at the center of the floor joist. If dimensional lumber is bowed or not squarely framed, the plywood or OSB will not catch a portion of the floor joist, causing the edge to float and feel like a weak spot.

3. Cupping Floorboards Due to Moisture

A floorboard should be even, and therefore cupping is an indication of an underlying problem. The warping destroys its aesthetic appeal, subsequently lowering the house’s value. An uneven floor is not appealing to the eye. 

You might have noticed that your floorboards are curling in some areas. The moisture beneath the finished flooring can often cause them to separate. In such a case, you cannot outrightly bet that a problem in the subfloor causes the curling. It could be that the floorboards were not well fitted, thus allowing penetration of moisture. 

However, there’s a chance that an underlying problem in the subfloor is causing the weakness of the subfloor. 

You should check for moisture damage in the subfloor in such a case. If the subfloor is level and dry, the warping is likely due to poor installation of the finished flooring.

4. Cracked and Popping Tiles

If your tiles are cracking and popping up without reason, there is a problem. A well-fitted tile should not easily come out. However, it is common for a few tiles to peel off, especially after extended use, but frequent cracks are due to a subfloor issue. 

You should check if the popped tile has no trowel marks. If it features a thin, dry set and no marks, that’s a huge red flag that there is a problem beneath. Most probably, there is an accumulation of moisture in the subfloor. 

However, it could also be due to the incompatibility of the tile and the subfloor material. Ideally, it would be best to have a cement board covering on top of the subfloor before laying tiles. It facilitates the creation of a firm platform that can firmly support the tiles. It also reduces the bounce that leads to the cracking of tiles. 

It does not matter what could be causing the cracking or popping. If you notice it, your subfloor has a problem, and you should fix it. Otherwise, your tiles will keep cracking. 

5. Musty Smell

A smell coming from the floor shows that there is wet wood and mold growth, most probably on the subfloor. It indicates that there’s a section where water has accumulated beneath. A damp crawl space is an ideal environment for mold growth. 

The first sign of mildew growth will be a musty smell. By the time you get the smell, the damage underneath will have already occurred. This issue is prevalent in bathroom subfloors or areas with frequent moisture exposure. 

Musty smells from a crawl space are typically caused by either a groundwater issue or a plumbing leak. Either condition left unchecked can cause substantial damage to the floor structure and subfloor.

For chronic groundwater issues, in addition to replacing wet subflooring, you will likely need to install a vapor barrier, dehumidifier, or crawl space encapsulation.

For plumbing leaks, you may be OK with just repairing the leaks and replacing the subfloor damage.

In cases where subfloor damage is minor, your contractor may add additional bracing between the floor joists to support the subfloor rather than subfloor replacement.

There is no way to replace the subfloor from underneath. You can only brace it to add structural support. Some contractors will brace the subfloor by adding bracing blocks between the floor joists or cut a thin piece of new plywood or OSB to press against the damaged subfloor and then brace it for support.

6. Bouncy Floor

If your floor gives you a springy feel as you walk, there is every reason to worry about the status of its subfloor area. Also, you may notice that the floorboards are shifting as you walk. It is also not normal and indicates a problem in the subfloor area. 

A spongy surface means a disjoint between the floorboards and the subfloor. Most probably, the subfloor is loose and cannot adequately absorb the pressure from above. Hence, the solution to bouncy floors is to check the status of the subfloor and fix it if it’s problematic. 

However, a bouncy floor will likely point to one of two conditions:

  • the crawl space has a moisture problem that has resulted in dry rot to the floor structure
  • there is a failed foundation support

7. A Loose Toilet 

A toilet should firmly fit on the surface. A toilet moves if the subfloor area is weak, and thus its anchors can barely hold it firmly. In most toilets, the subfloor damage is due to moisture resulting from leaky pipes. 

Fix the issues immediately when you notice the movement of your toilet. It will go a long way in preventing future damage. You will need to repair the damaged subfloor and the leaky pipes to prevent the recurrence of the issue. 

Moisture damage can also affect other parts of your floor, especially zones close to your main door. If the door is not well fitted, it will most likely allow moisture from rain or snow to permeate into the subfloor. 

Also, subfloor damage resulting from moisture is typical in areas that experience frequent flooding. Thus, instead of repairing your subfloor now and then, make your house waterproof first. It will go a long way in limiting moisture accumulation, which can be devastating. 

8. A Leaky Ceiling

If your ceiling is leaking, it can damage your subfloor. The subfloor absorbs water as it falls from the ceiling for severe roof leaks. Long-term exposure like this can lead to replacing your subfloor.

Therefore, replace the subfloor it is damaged from a roof leak. The wet subfloor can dry and not require replacement if you’re quick to action. Wood rot in the subfloor occurs from moisture exposure over time.

What Causes Subfloor Damage

From the above section, it is apparent that excess moisture exposure causes most subfloor damage. It could be due to a leaky pipe or flooding. Also, a poorly sealed door or window will, without a doubt, allow entry of moisture. 

It could also be due to the poor fitting of the toilet. In such a case, water from the toilet will leak and find a way to the subfloor. 

While most subfloor damage can be attributed primarily to water, other causes are. The US Department of Housing and Urban Development cites a pest infestation as a cause of damage. Also, exposure to frequent earthquakes will weaken the subfloor. Additionally, it could be due to issues with your floor’s foundation. 

It’s noteworthy that subfloor damage occurs in parts. Thus, It’s unusual to find a subfloor totally in all the parts. Therefore, repair should not be a big issue, especially if you detect the cause and the part where the damage is. 

We have listed the common telling signs above. They should guide you to identify when to call a flooring expert.  

Can You Replace the Subfloor Yourself?

If you have expertise in carpentry, you should have no problem replacing the subfloor. However, it would be best to engage a professional because fixing the issue is not simply a one-off thing. 

An expert will figure out the degree of damage and the cause. What may seem like a simple subfloor problem could be a significant issue. You could know something about subflooring, but a professional will handle it better, especially if it escalates to a compound issue. 

In addition to expertly identifying the cause and extent of damage, a professional has the right tools for the job. Having the right tools and expertise is critical in doing a perfect job. Hence, let a professional handle it, and rest assured that every problem will be highlighted and sorted. 

You still have a part in protecting the subfloor from damage. For instance, you can identify and fix the source of water that’s leading to the floor damage. For example, you might note an issue with the fitting with the door that you can fix without requiring expert assistance. 

According to the Environmental Protection Agency, you have to look for possible leaks as a homeowner. Quickly identifying and solving leaks will limit the probable repair costs to fix any damage. 

Therefore, as much as you should delegate subfloor repair to a professional, you must also be actively involved in its maintenance. 

How Much Does It Cost to Replace a Subfloor?

According to Angi, replacing a subfloor will cost approximately $500 for a space measuring 300 square feet. The cost could rise to $700 if you replace the subfloor in a larger room. Other vital aspects that can increase the cost include the material of choice and labor cost. 

The higher the quality of the material, the higher the costs. The cost could rise to $900 when you factor in the labor costs. On average, an hour’s work is around $30. Hence, you must be ready to shoulder the labor costs. 

What is the Cost Per Square Foot?

On average, the cost of most materials is in the range of $1.50 to $7 for a square foot. The price is reflective of the quality of the material. The cheapest material is plywood which will cost you an average of $1.5 per square foot. Hence, a room measuring 300 square feet will cost you $450. 

Much of the data online can be outdated, with rising building costs and material shortages. Material costs have more than doubled from 2019 to 2021. As of this writing, plywood ranges from $45 to $75 a sheet, and OSB ranges from $28 to $60 a sheet, depending on location.

For example, today, we estimate that you can expect to pay about $2.50 to $5 per square foot to replace a plywood subfloor at today’s prices.

What is the Cost of a DIY Subfloor Repair?

Are you a DIY enthusiast? If you like to handle fixes around your house, you can undertake the project. Nonetheless, as earlier advised, you need to be conversant with subfloor fixing. 

The fundamental upside of repairing the subfloor is that you’ll save on labor costs. Therefore, you will only need to spend on the material. Depending on your planned expenditure, select the material of choice. 

You will also need to buy the necessary tools though you probably have them. You need a circular saw that costs at least $40. You also require a crowbar that will cost you at least $10 and nails cost at least $10. Lastly, you will also need a nail gun which costs $150

We recommend using 1-1/2 inch screws over nails to replace the 5/8 inch OSB subfloor. Use 2-inch screws when you replace 3/4 inch plywood.

While you will save on labor costs, you’ll have to invest your time in the project. The time spent will depend on the extent of the subfloor damage. On average, you’ll spend about a whole day replacing the subfloor in one room. 

However, although doing it yourself will save you quite some labor costs, you’d instead hire a professional. They will choose the suitable material for your subfloor. A professional will also fix it faster than you would. 

A professional will cost you an average of $30 per hour. The average total cost of labor is between $720 and $3,200. Among the things that would increase your labor costs include moving stuff from the house and removing the old subfloor. 

Also, if your room is large, you will spend more on labor than on a small room. 

How Long Does it Take to Replace Subfloor?

An expert will replace a subfloor in no time, especially if the room is small-sized. However, if you choose to do it yourself, it may take up to a week to remove the old subfloor and fix the new one. 

A small room should not take more than 8 hours to fix for a professional. If the area is large, a maximum of 24 hours is enough to get the job done. Hence, that is why we insist that you should hire a professional to do the job. 

Is it Hard to Install Subfloor?

It is not difficult to install a subfloor if you have all the necessary tools. Anyone with basic carpentry skills will, therefore, quickly solve the issue. It may seem quite an ordeal at first, but everything should be seamless if you follow the necessary steps. 

We’ll list the key steps that are handy in fixing the subfloor:

You’ll Need to Assess the Damage

The best way to check the severity of the problem is to have a clear view of the subfloor area. It means that you will have to remove a part of the finished flooring. Once removed, use a spotlight to check the extent of the damage. You may also have to check the crawl space if the subfloor in the area is faulty. 

The inspection will get you set for the job ahead of you. Ideally, choose the least invasive technique of accessing. It will be cheap and also easy to execute. Nonetheless, depending on the extent of the problem, you may be compelled to remove a large subfloor area to determine what’s causing the problem. 

If you are dealing with a cracked tile issue, remove a particular time first to check the state of the subfloor underneath. 

You’ll Need to Determine the Cause 

Identifying what is causing the problem is the most vital step in the subfloor replacement process. If you don’t solve the cause, it will be futile to install another subfloor as it will suffer a similar fate to the first.  

If you are dealing with a toilet’s subfloor, check for leaking pipes. Your subfloor could also be warping because of improper installation. Hence, you should rectify that when laying the new subfloor area. 

Sometimes, the joists can also break, and it could cause subfloor damage. Once you identify the cause, it will be easy to fix the problem. 

Repair any Plumbing Leaks

If you ascertain that the subfloor damage is because of a water leak, fix the leak first. We’ve highlighted the essence of this step in the prior section. 

There are water problems that are beyond repair. When dealing with a leak issue, the most important part is identifying the duration of the leak. If the subfloor has been constantly in constant contact with water, it is not salvageable. The presence of mold is one of the indicators of a subfloor that is beyond repair. 

Thus, check out if there is a sign of extensive damage to the subfloor. But the source of the water leak is as important as the extent of the damage. For instance, the leak may be due to a water spill. Also, it could be that there was flooding in the house that led to the soaking of the subfloor. 

If the water problem was a one-off thing, you do not necessarily need to replace the entire subfloor. In such a case, the following remedies will help. 

  • Allow air to enter the affected areas by leaving all the furniture and coverings such as the carpet. Also, it is imperative to mop up all the water from the surface to hasten the drying process. 
  • If the drywall is wet, you also need to remove it. It will be handy in allowing the subfloor to dry fast. 
  • Getting the affected area aerated is also imperative in aiding the drying of the subfloor. For this, you’ll need to have box fans in the room. Make sure to use the box fans below and above the floor to fasten the drying process. We recommend the Hurricane Box Fan for this task. It is efficient and does not occupy much space in the house. It also features quite incredible speeds and can go up to 2400 CFM. 

Repairing Dry Subfloor Damage

You may have a scenario where the water damage has already dried, but parts of the subfloor material feel soft. You can strengthen the subfloor layer and thus avoid removing it, which is relatively tedious and pricey. However, ensure that the old layer doesn’t have a mold infestation. 

First, ascertain that there are no signs of mold or mildew growth. Next, connect a joist material on the underside of the subflooring material. After this, you can lay a new sublayer on top of the old subfloor without compromising the joist’s strength. 

Steps to Installing a New Subfloor

In other cases, you might find that the leak has been happening for an extended period and the subfloor is unsalvageable. In that case, you will have to replace it. But don’t be hasty in making a complete overhaul of the floor. Just fix the damaged part, and all will be well. 

Here is the procedure to follow in replacing your subfloor: 

  • First, remove the upper flooring material. It can be reusable or not, depending on the extent of damage that you are dealing with. If you deem it fit for reuse, make sure you remove it carefully to prevent damage. 
  • Remove the damaged subfloor and replace it with new material. During this phase, it is essential to ensure that you remove all the destroyed subfloors. If you leave some part, it will instigate the spread of mold to the new part.
  • Cut square symmetrical parts of the old subfloor. It will ensure that you can perfectly fit in the new subfloor without strain. 
  • When choosing the new subfloor material, ensure that it is of similar thickness to the older one. It will ensure that it fits perfectly on the joists. Next, apply an adhesive on the sides of the floor at the part where it is connected to the joists. We recommend Loctite PL Premium adhesive for this task as it is compatible with most subfloor material and other floorings.  Apply it using a caulking gun to obtain a thin, uniform even layer. 
  • Lay the subfloor and screw it firmly. If your floor was creaking before, it is now time to make the connection as tight as possible. You can also use nails, but they are prone to creaking. Hence, opt for screws. 

Also, remember that having a cement board layer is imperative if you want to lay a tile floor. At this juncture, you should screw it on the subfloor layer. 

Do You Need a Permit to Replace Subfloor

A permit is generally not required for replacing an isolated area of the subfloor. However, you should check with your local building department to ensure no other rules or regulations might apply to the project.

Subfloors are installed over a floor joist or engineered floor system. If the subfloor has rotted or is damaged to the point that it needs a full replacement, a permit will be required.

If you plan to replace some of the joists as part of your project, you will need a permit depending on local code requirements. The building department may require an inspector to check your subfloor after installing new joists or engineered trusses.

Do Plumbers Replace Subfloor

Plumbers are specialty contractors that work on water and waste piping only. Plumbers do not typically replace subfloors. However, that’s not to say that some don’t.

Usually, you’ll hire a licensed contractor who’ll handle all the structural repairs, and he will subcontract the plumbing repairs to a licensed plumber.

If you hired the plumber directly, they would usually work in conjunction with a licensed contractor of your choice to make the necessary repairs.

Final Thoughts

Replacing a subfloor is easy, especially if you are fixing a small area. However, if you have a significant problem, you may hire a professional. We have highlighted the critical indicators that you often need to replace. 

We have also explained the critical causes of subfloor damage and how to solve them. You need to prevent the issue from occurring by fixing the causes first. Primarily, a water leak will cause subfloor damage despite how many times you fix a new subfloor. 

Fixing a subfloor is not an arduous task, and you can do it yourself. However, you will need to have the requisite tools for the job. Take the above insights into account, and you will not get anything wrong when installing a subfloor. 



Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.