How to Replace RV Roof Decking in a Small Section

Step on your RV roof and find one spot that gives a little under your boot? That spongy square is rotted decking, and the good news is you usually do not need a whole roof. A small section — a few square feet around a vent, an AC, or a seam — can come out and go back in solid in a day. But the soft spot you can feel is never the whole story. Here's how I replace a small section so it stays fixed.

Step 1: Find the leak first

Decking does not rot on its own. Water got in somewhere above or beside that spot — a cracked sealant ring around a vent, a failed AC gasket, a seam that opened up, a screw that backed out. If you replace the wood and leave the entry point, you just gave the next leak fresh lumber to eat. Find it, note it, and plan to reseal it as part of this job, not after.

Step 2: Open the membrane carefully

Remove whatever sits over the bad area — vent, cap, trim — and keep the screws and garnish in order. Work the membrane loose gently and fold it back past the damage if it will let go clean; if it won't, cut it in a neat square well into the sound area and plan on a proper membrane patch later. Either way, don't shred it — every tear now is a seam to seal later. Photograph the framing and anything under the deck before you cut.

Step 3: Find the real boundary

Probe the exposed decking with an awl or screwdriver. Sound wood resists; rot lets the tool sink in. Work outward from the soft spot in every direction until the wood fights back, then mark your cut lines a few inches past that, in a square or rectangle. Check the framing underneath while you're there — dark, crumbling rafters are a bigger job than decking, and you need to know that before the new panel goes down, not after.

Step 4: Cut square, and only as deep as the deck

Set your saw depth to just the thickness of the decking so you cut wood, not the framing or wiring below it. Cut on your marked lines and lift the bad section out. If a cut edge lands between rafters with nothing under it, add blocking screwed to the framing so every edge of the new panel has something solid to bite into. A panel edge floating in air will flex, work its fasteners loose, and telegraph through the membrane.

Step 5: Match the original thickness exactly

This is where small roof jobs go wrong. RV decking is not one standard thickness — plenty of roofs are thin luan around 1/8 inch, others run 1/4 or 3/8 inch plywood or OSB. Measure the piece you took out and match it. A panel that's too thick stands proud and holds water against the seam; too thin and it dips and ponds. I prefer exterior-glue plywood with a smooth, sanded face for a patch the membrane has to bond to — rough OSB is a poor gluing surface on a small repair. Dry-fit the panel before any adhesive comes out.

Step 6: Fasten it down flat

Screw the new section to the framing and blocking, snug and flat, with the screw heads set just below the surface so nothing prints through the membrane. Work from the middle out so the panel seats evenly. Run your hand across every seam: if you can feel a lip, fix it now, because you will absolutely see it through the finished roof.

Step 7: Put the membrane back and seal it once

Bond the membrane back down with the adhesive made for your membrane type — EPDM and TPO are not interchangeable, so match the product to the roof you actually have. If you cut a square out, lay a patch that extends well past the cut on every side, roll it down flat, and seal the edges. Reinstall the vent or trim you removed on fresh butyl tape, then cap every screw head and seam edge with Dicor 501LSW-1 self-leveling lap sealant. On a suitable seam, EternaBond RoofSeal tape can be a belt-and-suspenders finish, but only on a clean surface it is rated for — never over old silicone or dirt. Then hose-test the whole area hard before you call it done.

When a small section is not a small job

• The rot runs past one bay of framing in several directions, or a rafter or truss is soft.
• The soft area keeps growing as you probe — that is a full tear-off conversation, not a patch.
• The ceiling below is stained or sagging, which means insulation and interior paneling are wet too.
• You find mold through the cavity. Dry it fully or cut further; never seal wet wood under new decking.

Done right, a small decking section is an honest day's work: find the leak, cut back to solid wood, match the thickness, support every edge, and seal it like you never want to see it again. That's the whole secret — fix it right the first time, and that soft spot is off your list for good.

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