How to Replace a Rotted Bathroom Floor & Subfloor

Suspecting that your Bathroom Floor & Subfloor might be Rotted due to Water damage?

In this guide you will learn:

  • Common Causes of Rotted Bathroom Floors
  • How to tell if your Subfloor has Started to Rot and if it can be repaired or will need to be replaced completely.
  • How to Repair & Replace Rotted Bathroom Subfloor & Flooring.

Rotting Bathroom floors can pose a serious risk to the safety of you, your family, and the structural integrity of your home. 

Bathrooms in particular are at greater risk of water damage than most other rooms in the house, and when wood gets wet it becomes prone to rotting.

Most Common Causes Of Rotted Bathroom Floors & Subfloors

Given that the bathroom likely has more plumbing in it than most other rooms in your home, the most common cause of rotted flooring and water damage is going to be leaks. 

Even simple things like splashes and tub spills can lead to serious water damage if left ignored, so it is important to get them cleaned up right away.

Cracks in your pipes and plumbing can also lead to water absorbing into the wood, and could go undetected until the damage is already done.

If there’s a room beneath the bathroom, check the ceiling in that room. Dark spotting or discoloration could indicate a leak in the plumbing.

Another culprit could be an improperly sealed toilet.  Most toilets connect to the floor with a flange, which is then sealed with a wax ring.

If the wax ring isn’t properly installed or breaks, the toilet will leak, and most of that water will leak into the floor underneath. If you look around the base of your toilet where it meets the floor and the wood looks softened or discolored, chances are good there is a leak which has begun to damage the flooring underneath.

If left too long, the flooring will need replaced entirely. In the worst case, your Subfloor in the bathroom will need to be replaced as well.

How Do I Know If My Bathroom Floor Is Rotted?

Rotted subflooring is a result of unresolved and ongoing water damage. When water leaks or splashes are allowed to continue to accumulate, your flooring in bathroom will continue to absorb moisture, and over time as it remains in contact with the subflooring will begin to cause rot.

Signs of rotting bathroom subflooring include:

1. damp, musty smell

Rotting wood gives off a distinct, unpleasant odor, and is a good indicator your flooring and subflooring are beginning to rot.

2. Mold and/or mildew that keeps growing back

Ongoing moisture issues provide ideal conditions for mold and mildew to grow.

3. Warped floorboards and walls

When wood absorbs moisture, it swells and warps, causing uneven flooring and can even wick up into the walls.

4. Soft, squishy, or spongy flooring

As wood rots, it will become soft and spongy, causing the flooring to feel soft or have an abnormal amount of give to it when stepped on.

5. Noticeable gaps in the caulking between the tub and the floor, or the tiling

As the flooring continues to rot, things like tubs and tiling can shift, causing gaps to appear in the caulking which can lead to more water getting in and exacerbating the process.

Should You Repair Or Replace?

In most instances of severe water damage, the best option is to have the subflooring in your bathroom completely replaced. 

In some instances where the rot is only surface-level and in a small area cutting out the affected area and replacing it with new plywood/floorboards will make more sense.

In cases of serious water damage and wood rot that has taken over all your subfloor in the bathroom, replacing is the safest route to go.

Once wood has begun to rot, the damage is irreversible.  When wet, wood begins to grow a certain type of fungi that feeds off of the moisture, which in turn destroys the wood as it does so. 

This process is detrimental to wooden flooring, subflooring, and floor joists.

If rot has begun to take hold of your floor joists, a repair simply isn’t viable. They will need to be replaced.  The floor will no longer be safe, as it will begin to sink, and could even become compromised completely over time.

Water Damaged Bathroom Floor or Subfloor?

Call 844-488-0570 for a Risk Free estimate from a Licensed Water Damage Restoration Specialist in your area.

We Can Help Assess the Damage & Repair / Replace your Subfloor.

How To Replace A Rotted Bathroom Subfloor

Replacing a Rotted Bathroom Floor / Subfloor can take anywhere from 8 to 24 hours of actual labor time, so you’ll want to plan in advance so you have enough time to finish

Before you begin you’ll need to turn off the water to the bathroom. You should also consider cutting the power to the bathroom via your breaker box, if possible, to eliminate any risk of electric shock.

Before beginning, you’ll want to also gather some tools and materials such as:

  • A circular saw
  • A variable speed drill for driving screws
  • A measuring tape
  • Chalk
  • A claw hammer
  • A pry bar
  • Spare hardware, such as nails and screws, 2 to 3 inches thick depending on your subflooring
  • Sheets of Plywood the same thickness as your current subfloor if you have plywood subfloor & if you plan to only replace some areas.
  • New Floorboards if you your subfloor isn’t plywood.

As always, be sure to wear necessary protective gear such as safety glasses, and follow all manufacturer instructions and precautions when using power tools.

Once you’ve gathered your tools and materials and have replacement plywood to replace the rotten areas, the process to replace your rotten bathroom subfloor can be broken down as follows.

1.Remove fixtures as necessary

First and foremost, you’ll need to remove any bathroom fixtures that might be in the way if the area beneath them has been affected. 

This can include toilets, sinks, cabinets, and even bathtubs or showers in some instances.

If you’re planning on doing a remodel anyways, removal should be relatively easy.  But if there are fixtures you want to save, this can become complicated very quickly. 

Be as gentle as possible with anything you want to save, and make sure you have a new wax ring and bolts ready in case you have to remove the toilet.

2.Remove flooring and underlayment

The easiest way to remove the bathroom flooring is usually to start at the wall, and work your way inward.  Remove the moulding along the wall (again, doing so carefully if you’re intending to reuse it), then start sliding out planks if it’s a floating floor.

If it’s a flooring that’s nailed/glued down using a crowbar or claw hammer, pry up the old flooring. If you’re removing laminate, you may need a scoring tool of some sort. 

If your bathroom has ceramic tile floor, chances are its going to break when you remove it, so it’s probably best to plan on replacing it

But if you’re intent on trying to save it, you can attempt to do so by removing the grout first with something like a grout saw or utility knife, then working the tile loose with a putty knife.

Once the bathroom floor is up, the underlayment should be exposed, which can be removed almost as easily.  Unlike subflooring which runs the length of the house, underlayment is specific to each room, and hopefully acted as a barrier to prevent damage to the subflooring. 

It may take some elbow grease if it’s been glued down, but in the event of nails a claw hammer will do the trick.

3.Assess damage to the subflooring

With the subfloor exposed, this is when it comes time to see the severity of the wood rot in your bathroom subfloor & deciding whether the subflooring needs to be completely replaced or only some areas of it.

Any signs of water damage or rot to your subflooring should be taken seriously, and when deciding whether to replace it’s always best to err on the side of caution.

If the rot has gone all the way through the bathroom subflooring and is completely rotten, removing it so it can be replaced will be necessary.

If there are visible signs of mold or mildew in the wood, you’ll want to use caution while working in the area. 

Check the areas around where your toilet is/was at this time, and see if it will need replaced as well.

Toilets are one of the most common culprits of rotten bathroom subfloors.

Anywhere you see signs of water damage should be assessed to ensure the structural integrity hasn’t been compromised, and you should always prioritize your family’s safety over cutting costs in materials.

4.Check plumbing for functionality

With the flooring removed, now is also a good time to inspect the visible plumbing of your bathroom.  Spotting signs of leaks and other water damage should be easier now. 

Look around where the toilet and sink were installed in particular, as those are often problematic areas.

If you removed the tub and/or shower, now would also be a good time to check that plumbing for leaks as well. In the event of cracked or severely damaged plumbing, it might be worth considering if its time to call in a professional for help. 

Replacing the flooring will be for nought if it’s just going to get wet again.

5.Remove and replace subflooring where needed

Subflooring generally runs across the span of the house and underneath walls, so removing the damaged section is going to take some cutting, which is where the circular saw comes into play.

If planning to replace only a smaller section of your rotten bathroom subfloor we will need to cut out the rotten areas and replace them with new plywood or floorboards.

We will focus more on replacing Rotten Plywood Subfloors, the process will be almost the same for floorboards.

  • Measure carefully while making note of the dimensions (write these down), and use chalk lines to outline the area that needs cut.
  • While cutting, follow the chalk lines carefully and be sure to wear safety glasses to avoid any incidents involving flying splinters.
  • Ensure that each cut bypasses an intersection with an adjacent cut by about an inch so that it cuts completely through the plywood. 

Once all cuts have been made, remove the section of plywood subflooring.  If nailed down, a claw hammer will be your best bet, but if glued this may require the use of that prybar again.

Now that the joists are exposed, take time to inspect your floor joists, and ensure they haven’t begun to rot as well.

Unfortunately floor joists can’t be repaired in the same manner as subflooring, and if they are water damaged or showing signs of mold will need to be replaced, sometimes new floor joists can be ”sistered-in”.

If they’re damaged and need to be replaced, this is definitely a point where you should consider calling in a professional.  Replacing joists can be dangerous work, and if done improperly can be a major safety hazard for you and your family.

If you see any signs of mold or mildew, now is the time to address that as well.

Next, you’ll want to cut a piece of new plywood using the dimensions you gathered earlier (you wrote them down, right?).  Make sure you measure carefully because this will need to fit into the hole you just created.

Lastly, affix the newly cut plywood on top of the joists, and screw it down using the drill and screws.  Make sure you’re screwing in to the floor joists, and keep the screws roughly 4-6 inches apart.

If the water damage is severe and all of the subfloor in your bathroom is completely rotted and needs to be replaced, this will require taking up/sawing out all of the subfloor and replacing it with new sheets of plywood.

6.Putting everything back in place

Once this is all finished, the whole process resumes in reverse.

Start with the new underlayment, and secure it to the new subflooring much the way you secured the subflooring to the joists. 

If the toilet needed reseating, now is the time to install the new flange and ensure the wax ring is set properly.

Based on the type of tub you have, this might be a good time to reinstall it as well. Doing so will prevent it from scratching up the flooring when applicable, and will make waterproofing the edges around it easier and more effective.

Once this is done and the underlayment is secured, you can begin reinstalling the flooring.

Depending on what kind of flooring you had, this could be as easy as sliding boards back into place, or laying down new laminate. If your bathroom floor was tiled, this unfortunately means laying down the new tile, in which case you should follow all tile laying guidelines to ensure a watertight seal between them.

With the floor back in place, installing remaining fixtures such as sinks, vanities, and toilets should be a relatively easy process. 

Ensure all seals are watertight when reassembling any plumbing beneath sinks, and use caution when nailing molding back into place along the walls. 

If you’re installing laminate or hardwood of any kind, be sure to leave a gap for expansion beneath the molding, and allow the wood to properly acclimate to the room beforehand.

Subfloor Needs Replacing?

Call 844-488-0570 for a Free estimate from a Licensed Water Damage Restoration Specialist in your area.

We Can Help Assess the damage & Repair/Replace Water Damaged Subfloors.

How Much Does It Cost To Replace Rotted Bathroom Floor & Does Insurance Cover It?

On average, replacing a plywood subfloor costs between $800 and $1600 in a 300 square foot bathroom. 

Depending on the size and complexity of your bathroom’s floor layout as well as the local contractor rates, you could be looking at spending more or less.

This will also depend if you are replacing the whole subfloor in your bathroom or only some parts of it need to be cut out/replaced.

If doing yourself, You’re looking at a range of $3 and $7 per square foot for materials, more if you decide to spring for high end material or if you have floorboards instead of plywood as your subfloor. It’s important to remember that there will be additional costs of labour/material if you also need your flooring replaced.

If you find out that your Floor joists are also rotten and need to be replaced in the bathroom, this can skyrocket the prices!

In the event of water damaged subflooring that needs replaced, homeowner’s insurance will usually cover subfloor replacement if it’s due to recent water damage & Not negligence.

When consulting with a contractor, contact your insurance company to determine whether replacing the subflooring will be necessary and whether or not it will be covered by your insurance.

Can I Replace The Rotted Subfloor And Flooring Myself?

Replacing your own rotted flooring and subflooring is possible, but will require some specialized equipment and materials. If you feel confident in your ability and have access to the necessary tools and equipment/materials needed, it is entirely feasible to replace the rotted subflooring yourself.

One thing to bear in mind, however, is that subflooring typically runs in a continuous sheet underneath the walls.  In order to replace it, you’ll be looking at sawing out damaged portions of the subflooring, and potentially replacing damaged floor joists as well.

Again, this can all be done with some proper research and no small amount of patience, but should be given the proper consideration when deciding whether to take on this project yourself.

When To Call A Professional

Water Damaged subfloors & floor joists can lead to serious structural issues, and need to be properly repaired to ensure the safety of your bathroom floor.

If you ever find yourself questioning the integrity of your floor joists, that is a fairly clear indicator it’s time to get professional help or at least an assessment.

If there is serious wood rot in your bathroom subfloor, the chance is you will need to replace all of the subflooring which often is best left to a professional.

Even if you’ve already started the repair yourself, if at any point you feel like you’re doing more damage than good, stop and contact a professional.  Doing so could prevent more serious damage from being further incurred, and could prevent more costly repair bills in doing so.

We have Water Damage Restoration Technicians that can help take care of your Rotten / Water Damaged Bathroom Floors/Subfloors.

For Disasters of all Sizes,available in 95% of the USA


Scroll to Top