RV Roof Soft Spots: What They Usually Mean

You’re up on the roof clearing leaves, you take a step, and the surface gives a little more than it should. Most owners do exactly the same thing next: press it a few times, decide it’s “probably fine,” and climb down. Here’s what that spot is actually telling you.

What’s under your feet

The membrane you’re standing on has almost no structure of its own. It’s glued to a thin decking layer — often 3 to 5 millimetre luan plywood, sometimes OSB — which spans framing members spaced somewhere between 16 and 24 inches apart. When decking gets wet, the glue lines between its plies let go and the sheet turns from a stiff panel into layers of damp cardboard. That’s the softness you feel. The membrane above it can be completely intact; the water usually arrived sideways, from a seam or penetration nearby.

Normal flex vs. a real problem

Lightweight builds flex a little between framing members, and a hot day makes every roof feel softer. So calibrate: walk the same spot on the opposite side of the roof. Symmetrical give is construction. One spot that feels mushy, crackles faintly, stays depressed for a moment after you step off, or is clearly different from the rest of the roof — that’s not construction.

Where it goes if you leave it

Wet decking doesn’t dry out down there. The membrane seals it from above, the vapour barrier slows it from below, and the insulation beside it holds water like a sponge. Rot spreads along the plies under perfectly good rubber, every step you take flexes the weakened sheet a bit further, and each winter’s freeze-thaw pries the delamination wider. A soft patch the size of a dinner plate in June has a way of becoming a quarter of the roof by the time it shows up inside.

Why the repair math punishes waiting

Replacing decking means opening the roof — membrane up, bad wood out, new decking in, then proper sealing over the repair. The cost scales almost linearly with area. A one-sheet repair caught early is a manageable job; the same rot after two more seasons can involve framing, insulation, the ceiling panel below, and a much harder conversation about whether repair still beats replacement.

What a proper assessment looks like

Not a thumb-press and a shrug. Moisture-meter readings to map how far the wet actually extends (it’s reliably bigger than the soft area), a check of the nearest seams and penetrations for the entry point, an interior look for staining and smell, and photos of all of it. Then you get options in order: fix the leak, repair the structure, reseal to protect the repair. Sealing over wet wood is the one move that’s always wrong — it just locks the problem in where you can’t see it work.