RV Floor Replacement: How to Fix Rotting Subfloor

Before touching the floor, find what caused the rot. A rotten RV subfloor is almost always the result of a water intrusion — a failed roof seal, a leaking window or door gasket, a deteriorated slide-out seal, or a plumbing leak. Inspect the rotten area closely and check the walls, windows, roof, and any nearby water lines or drain pipes.

Fix the leak before you fix the floor. Replacing the subfloor without addressing the source of the moisture is wasted effort — the new wood will rot exactly the same way the old wood did.

Once the leak is repaired, check the entire RV floor for additional soft or spongy spots. Water travels, so the visible damage is rarely the only damage. Walk the full floor pressing down with your foot, and probe suspicious areas with a screwdriver. Any give, sponginess, or discoloration in the subfloor indicates rot.

Mark all soft spots before you start cutting. Once you’ve mapped the damage, cut and peel back the laminate, vinyl, or carpet to expose the subfloor beneath. Some owners cut carefully along the wall to preserve the flooring for reuse. Either way, keep peeling in all directions from each soft spot until you reach solid, undiscolored wood on all four sides.

Use a small handsaw or circular saw to cut through the rotten subfloor and a pry bar to remove the pieces.

A few important notes:

If foam underlayment is present, remove only the wood — not the foam. The foam provides insulation and structure; preserve it where possible.

If wooden floor supports run beneath the subfloor, cut the removal area to a rectangle that aligns with supports on at least two sides. This gives you solid attachment points for the new subfloor piece.

Remove everything damaged. Leaving any rotted wood in place gives the new wood something to rot against. Be thorough.

With the rotten material removed, allow all exposed wood framing and surrounding subfloor to dry completely before proceeding. Depending on how saturated the wood is, this can take a week or more. Running a fan or dehumidifier in the space speeds the process.
Installing new wood over damp framing or subfloor can recreate the same conditions that caused the rot in the first place.

Note: If the wood frame itself is rotten, you’ll need to remove and replace those sections. This requires basic carpentry skills — if that’s beyond your skills, this is the point to bring in a professional. Similarly, if any styrofoam underlayment is waterlogged, replace it before proceeding.

Once the wood is dry, treat any remaining mold or rot organisms in the surrounding wood before sealing.

The best options:

Borax solution is the most practical and cost-effective choice for most DIYers. Mix 1 cup of borax (20 Mule Team, available at most grocery stores for around $8) with 1 gallon of hot water, apply with a spray bottle or brush, and let it penetrate. Borax is a proven borate-based fungicide that kills mold organisms and helps prevent recurrence. It’s significantly cheaper and safer than antifreeze and works better on established mold. Allow the wood to dry thoroughly after application.

Commercial borate products like Timbor or BoraCare are professional-grade versions of the same chemistry, often used by restoration contractors. They are more expensive than DIY borax but deeply penetrating and highly effective for serious infestations.

White vinegar (undiluted) is a reasonable option for surface mold on accessible areas — spray, let sit for an hour, and wipe clean.

A note on antifreeze: Some older DIY guides recommend applying ethylene glycol (automotive antifreeze) to kill rot organisms, and it does have some antifungal properties against wood-destroying fungi. However, it’s not recommended here for several reasons: automotive antifreeze is highly toxic and potentially fatal to pets even in small amounts, it leaves a residue that interferes with adhesives and sealants, and safer and more effective alternatives are readily available and cheaper. If you do choose to use it, use only non-toxic RV antifreeze (propylene glycol-based, pink label) and follow all safety precautions carefully.

Now seal the wood around the repaired area to protect against further rot, strengthen any compromised wood fibers, and create a moisture barrier.

Epoxy consolidant (Git Rot is a well-regarded option) is ideal for this. Combine the two-part system according to the manufacturer’s instructions, then brush or spray the mixed solution over the wood surrounding the repair area. For maximum penetration into compromised wood, inject the epoxy directly into the material using a syringe. Depending on the hardener, you’ll have minutes to an hour of working time before it begins to set — full cure takes up to two weeks.

Kilz mold-resistant primer is a worthwhile second layer of protection, particularly in areas prone to recurring moisture. It’s widely available, easy to apply, and provides an additional mildew-resistant barrier before the new subfloor goes in.

Safety note: Epoxy fumes are harsh. Work only in a well-ventilated space. Wear disposable gloves and a respirator throughout mixing and application.

Cut a replacement piece of plywood that matches your existing subfloor in thickness — this is critical for keeping the new surface flush with the surrounding floor. Measure twice, cut once, and aim for a fit as precise as possible.

If wooden framing runs beneath the subfloor, add cross supports before installing the new piece — it gives the new wood additional stability and reduces flex over time. Apply wood glue to the underside of the new piece (or to the top of the foam if that’s what’s beneath), set it in the hole, and screw it into the support framing below.

Sand the edges of the new piece where it meets the old subfloor until the transition is flush. Use sealant or caulk to fill the seam between old and new wood, and allow it to cure completely before covering.

With the subfloor solid and sealed, you’re ready to finish the surface. You can reuse the original flooring if you cut it carefully in Step 2, but a subfloor repair is a natural opportunity to upgrade.

Vinyl plank or sheet vinyl is the best choice for bathrooms, kitchens, and entry areas — waterproof, easy to clean, and forgiving in high-moisture zones. Modern vinyl plank options are durable and look far better than the vinyl flooring of a decade ago.

Laminate plank (luxury vinyl plank or LVP) is the most popular current choice for RV interiors. It mimics hardwood, handles moderate moisture better than traditional laminate, and works throughout the entire rig. Add area rugs in the bedroom and living area for warmth and comfort.

Carpet works well in bedrooms and living areas where moisture exposure is low, but is a poor choice for anywhere water, mud, or spills are likely.