How to Replace Your RV Subfloor If You Find Water Damage

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If water damage finds you, it’s time to replace your RV subfloor. Here’s what to know from an RVer who has been through the process.

Water damage can be so disheartening to find in your RV or camper. Where did it come from? How long has it been there? Is that mold? How bad is the damage? How do we fix it!? 

These were all questions that came to our minds when we found water damage in our RV slide-out floor. We noticed it starting to bow down the center, and then one day, my husband stepped on the edge of the slide, and the floor detached from the wall, and we could see daylight. 

He went outside and screwed the floor back in, but we knew that was only a band-aid fix, and the whole subfloor would need to be replaced.

Once we were settled into a spot with the space, tools, and help to complete an RV subfloor replacement, we got to work.

How to Spot Water Damage in Your RV

There are many different ways to spot water damage in your RV or camper:

• Wet floor
• Discoloration on subfloor or walls
• Water leaking from windows, vents, lights, or walls.
• Delamination
• Soft spots on floors or walls
• Wrinkled or peeling walls
• Rust-colored stains or rusty screws
• Musty smells
• Water pump running even when you are not using water
• Use a moisture meter

Assessing the Damage

Once you have spotted the damage, you must determine how bad it is and where it originated. This can be a tricky task—just because the corner of your floor is wet doesn’t mean the leak is right there. 

In our case, we found that the leak was caused by a tiny hole in the membrane on our slide-out roof and some bad caulking.

Some common areas to check for the source of a leak:

• Caulking. And I mean, check ALL of the caulking. Caulking around windows, vents, doors, and every corner of the camper. If there are any cracks or separations, water is likely entering there.
• Roof. Look for a tear or hole in the roof membrane and for any soft spots in the roof.
• Connections. Are all of your waterline connections tight? Any leaks when you hook up to city water? Does your water pump continue to run even when you aren’t using it?

It is very important to find the source of the leak and make the necessary repairs before fixing the damage it caused. Otherwise, you will likely find yourself in the same situation a little further down the road.

Determining if the Subfloor Needs to be Replaced

After we pulled up the vinyl, we could see how bad the water damage really was. And it was bad!

Both corners were rotted, and mold was all over the underside of our vinyl. There was no saving that vinyl. It went straight to the dumpster along with the entire moldy subfloor.

Mold Mitigation

You need to carefully remove any mold you find. There are a few different ways to do it. If it is on a non-porous surface, you can spray a mixture of either bleach and water or white distilled vinegar and water, let it sit for a bit, and then clean off with warm water.

For mold on wood, I would follow the steps detailed here.

If you aren’t sure if you have mold, you can also always do an at home test kit like this one.

Replace Your RV Subfloor

To replace your RV subfloor is a multi-day project. Since we were living full-time in our camper with our pets, we wanted to make the repairs as quickly as possible. We started by making the new floor first. 

To do this we had to begin by measuring our slide out floor. Ours was about 12’x4’ and 1” thick. Most subfloors are 1” thick, but some can be ¾”, so it is important to check this before buying your new subfloor. We were able to check our thickness by cutting a hole in the floor and measuring it before buying the supplies.

A 12’ x 4’ plywood board is not readily available at hardware stores unless you special order it.

We bought four 8’x 4’, ½-inch thick plywood boards and glued them together. We staggered the seams so we didn’t have one really weak spot.

The type of glue we used is not forgiving. Once the two pieces of wood touch, they are stuck, and there is no adjusting. For this step, we had one person on each corner of the wood to be extra meticulous as we attached.

While researching how to repair this ourselves, we talked to several RV repair shops to see how they replace a slide-out floor this big. They told us they would do it exactly the same way we were. 

We also asked the RV shop about replacing the black tarp-like material that was currently underneath our slide floor. They said they no longer use that, and they either put nothing underneath (we didn’t like the thought of that!) or they glue an FRP (Fiberglass Reinforced Plastic) panel to the bottom.

We ended up going with an NRP (Non-fiberglass Reinforced Plastic) panel instead of FRP, because it was more budget friendly, lighter weight, and not as stiff. We glued this to the bottom of the subfloor after cutting it to size. 

Removing the Old Floor

In order to remove the sub floor, you will first need to take off all of the fenders, trim pieces, and flashing along the bottom of the slide-out. Take pictures or make notes of where everything goes, because there will be a lot of it.

Next you will need to have a way to support the slide out once you bring in the slide mechanism. We screwed in a 2×4 board on each side of the slide out and supported them on 2 floor jacks.

Once it is supported you will need to disconnect the slide out bars from the floor, and bring the bars in. Next, you will need to remove the support bar that will be going across the front of the slide. This should be held on by large lag screws.

Once that bar is free, you can remove the rest of the screws around the perimeter of the floor. We had one person holding the floor up, while the other went around removing the screws. Most screws will be removed from the outside, but some RVs may have screws on the inside.

Now your floor is free to drop out!

Assessing the Walls and Studs

The walls and some of the studs will likely also have water damage. You will want your new floor to be mounted into sturdy, dry wood, so it is important to assess these as well.

We were lucky to only have to replace one small stud. Our wall was in decent condition, and we knew we would paint and put trim pieces on the wall when we were done, so we were not worried about that.

Installing the New Floor

This part was all hands on deck! This took some muscle and small maneuvering to get it exactly in place. We had family help us put the floor into place and hold it up while it was screwed in. Then we brought the slide out bars back out and reconnected them.

We also opted to add ski slides on each side for extra water protection, which the RV shop also recommended. However, one of them has already cracked after just a couple of months. I’m not sure if it was user error or a poor product.

Once we felt good about the new floor, we brought the slide in and out a few times to make sure everything seemed to fit and move ok. Once we were confident with it, we put all of the trim pieces back on and re-caulked everything.

Before installing the new sheet vinyl, we added a layer of insulation to help with temperature regulation in the camper. We were also able to find new vinyl that was a very close match to the original in the camper.

We did not glue down the insulation or vinyl, so we will be able to periodically pull it up in the corners to make sure we have no leaks.

Read More: Replacing RV Flooring: A Complete Guide For Removing and Installing

How Much Does Replacing RV Subflooring Cost?

Here are my costs:

• Plywood: $150
• NRP: $58
• Glue: $100
• Vinyl: $90
• Floor Trim: $72
• Insulation: $27
• Caulking: $20
• Misc Supplies: $40

Total Cost: $557

When we checked with an RV repair shop on how much it would cost for them to do the repair, we were quoted about $2000, and that did not include the new vinyl, insulation, or trim, or replacement of any studs.

It would also have to be in the shop for about a week, which would have meant we would also need to pay for a pet friendly hotel or airbnb for that week. 

I think we did pretty great on our own. Here’s the final product:

Does Insurance Cover RV Subfloor Repairs?

I spoke to our insurance agent to see if this was something that our policy covered, and unfortunately it was not. He said if the damage was caused by a one-time event such as a burst water pipe or a storm, then it would be covered.

But, since this was most likely caused overtime by wear and tear and/or lack of maintenance (i.e., not replacing old cracked caulking) it would not be covered. He said this would be the same for most camper repairs and most insurance policies. 

How to Replace your RV Subfloor If You Find Water Damage

This was definitely the biggest repair we have done so far in our camper, and we couldn’t have done it without the knowledge and extra muscle from our brother-in-law. We also watched a few Youtube videos to learn how others have gone through the process as well.

You can see the videos we made about this project on our Instagram or tiktok @the_path_we_take.

Replacing Your RV Subfloor

Replacing your RV subfloor is a major project, but it’s not unachievable for DIYers like us. I hope our experience helps you with your own RV subfloor replacement. Drop a comment if you have any questions!