RV Subfloor and Flooring Replacement

Where the water comes in and how far it travels

Floors rarely rot from spills. The water arrives from a failed seal somewhere above or beside, runs inside the structure, and collects at the lowest horizontal surface it can reach. The usual origins are a slide-out wiper seal that has hardened, a roof penetration around a vent or antenna, a window frame whose butyl has released, the shower pan corner, and the toilet flange. Each of them puts water into a cavity where evaporation is nearly impossible, and the plywood sits damp indefinitely.

Once moisture content stays above roughly twenty percent, the fungi that break down wood become active. The plywood does not fail evenly. The glue lines between veneers separate first, which is why the symptom is a floor that flexes and feels hollow rather than one that crumbles. That is delamination, and it means the panel has lost the layered structure that gave it stiffness even where the surface looks intact and dry.

The damage spreads much wider than the soft area. Water wicks along the grain and travels through the floor cavity, so a spongy patch at the entry door frequently indicates saturation running two or three feet in every direction under cabinets that show nothing at all. This is why probing before quoting is not optional. A repair scoped to the soft spot alone leaves compromised material in place and the new panel edges land on nothing solid.

Slide rooms deserve their own mention because they concentrate the problem. The seal has to accommodate a moving surface, it wears where the room passes over it, and the floor immediately inboard of the opening catches everything that gets past. On many floorplans that is also where the slide rails and support structure attach, so rot there compromises both the floor and the mechanism that runs across it.

Mapping the damage before anyone cuts

A pinless moisture meter reads through a finished surface and is where we start, sweeping a grid across the floor and up the lower walls to build a picture of where moisture is elevated. It is a comparative tool rather than an absolute one, so we establish a baseline in an area known to be dry and work from the difference. Elevated readings that extend past the area anyone suspected are the normal outcome, not the exception.

Pin probes come next in areas where a small hole will be covered by the repair anyway, because they read actual moisture content at depth and confirm what the pinless sweep suggested. Sounding with a mallet adds a third data point: delaminated plywood returns a dull, dead note against the crisp sound of intact material, and the boundary between those two sounds is usually more accurate than either meter alone.

From below, the belly wrap comes down. On a travel trailer that underbelly is a coroplast or vinyl membrane stapled to the frame, and dropping a section reveals the underside of the floor, the insulation, and often standing water in a batt that has been holding it for months. It also exposes the frame outriggers and whatever plumbing or wiring crosses the repair area, which has to be mapped before a saw goes in.

Cutting back, rebuilding, and what goes back in

Cuts are made back to material that reads dry and sounds solid, and they land over a frame member or an outrigger so the new panel has bearing on every edge. Where no member falls conveniently, we add blocking. Cutting to a straight line for appearance while leaving damp plywood beyond it is the most common shortcut in this repair, and it produces a floor that is soft again next to the patch within two years.

Material choice matters more than most owners are told. Original subfloor is frequently oriented strand board or a low grade plywood, and neither has much resistance to a second wetting event. We rebuild in exterior grade plywood, and in wet zones such as bathrooms and the area inboard of a slide we use marine-grade panel, which has no core voids and uses a fully waterproof adhesive. It costs more per sheet and it is a rounding error against doing the job twice.

On laminated floor construction, where the deck is a bonded sandwich of plywood, block foam, and a lower skin, the repair is different again. That assembly is structural in a way a plank floor is not, and a patch has to restore the sandwich rather than just fill the hole. We rebuild it in layers with structural adhesive and clamping pressure so the panel regains its stiffness, and we seal every cut edge, because an unsealed edge is where the next failure will start.

The last step is the reason for all of it. Whatever let the water in gets repaired before the floor closes up. Slide seals replaced, roof penetrations resealed with the correct product for the membrane, window frames rebedded, and the shower pan or flange corrected. We will not lay a finished surface over a repair while the source is still active, and if the source is outside the scope you approved we will tell you what it costs before we go further.

Choosing a finished surface that tolerates a moving building

Luxury vinyl plank is the most popular choice and for good reason: it is waterproof, it handles the dimensional movement of a vehicle body, and a damaged plank in a floating installation can be swapped. The critical detail is the perimeter expansion gap. A vehicle flexes and the floor moves relative to the walls, and a floating floor installed tight to the cabinets will buckle at the seams during the first hot week. That gap gets covered by trim or shoe, never filled.

Glue-down vinyl works well in tight areas and around slide openings where a floating field would be interrupted constantly, and it eliminates the hollow sound that a floating floor produces over a large open bay. It demands a genuinely flat and clean substrate, which is another argument for replacing rather than overlaying compromised subfloor. Adhesive selection has to account for interior temperatures that reach well above what a residential product is rated for.

Laminate with a fiberboard core is the one we steer people away from. The core swells irreversibly with any water contact, and an RV is a building that will get wet at some point in its life. Carpet remains reasonable in a bedroom slide where it deadens noise and never sees water, and tile is realistic only with a properly decoupled substrate, which most units cannot support without adding weight that the axles will notice.

What is included

Moisture mapping across the floor and lower walls

Pinless sweep against a dry baseline, pin probes at depth, and mallet sounding to fix the boundary.

Underbelly access and inspection

Membrane dropped to expose the underside, saturated insulation removed, and crossing plumbing and wiring mapped.

Cut back to sound material over bearing

Edges landed on frame members or added blocking so no new panel edge is unsupported.

Exterior and marine-grade panel replacement

Void-resistant marine panel in bathrooms and slide zones, exterior grade elsewhere, with every cut edge sealed.

Laminated deck rebuild

Bonded sandwich floors restored in layers under clamping pressure so stiffness returns rather than just thickness.

Source repair before closing up

Slide seals, roof penetrations, window bedding, or flange corrected so the new floor is not on borrowed time.

Signs you need this work

• A spot near the entry step or the slide opening that gives underfoot
• Floor covering that has lifted or bubbled in one area for no obvious reason
• A musty smell that is strongest with the storage bays closed up
• Staining or drip marks on the underbelly membrane below a slide
• Trim along the base of a wall that has separated or cupped
• A dull, hollow sound when you tap the floor in one part of the coach