How to Repair RV Roof Soft Spots: Fix Water-Damaged Wood Step-by-Step Guide

The Quick Answer

Your approach is exactly right - you'll need to cut back the rubber membrane around the soft spot, remove and replace the damaged decking material, then reseal with either a patch or larger membrane section. Since you're planning to replace the vent anyway and the damage is vent-adjacent, I'd recommend going with a larger rubber membrane patch that extends well beyond the repair area for the most durable fix. This type of repair typically takes a full day and costs $150-300 in materials, depending on whether you patch or do a larger membrane replacement.

What's Causing This

You've diagnosed this correctly - water infiltration around the vent has compromised the roof decking underneath your rubber membrane. This is extremely common with RV roof vents, especially older ones where the sealant has dried out or cracked. The soft spot you felt is likely rotted plywood or OSB decking that has lost its structural integrity from repeated wet/dry cycles.

Roof vents are notorious weak points because they create multiple penetration points through the membrane, and the sealants used (typically butyl tape and Dicor or similar) can fail over time due to UV exposure and thermal cycling. Once water gets underneath, it spreads along the decking and can affect a larger area than initially visible. The fact that it's a hand-sized soft area suggests the damage has been developing for at least one or two seasons.

The good news is that catching it before it breaks through means you likely don't have interior damage to deal with, and the repair will be much more straightforward than if water had been dripping into your RV's interior spaces.

Tools You'll Need

Safety first: Working on RV roofs requires proper fall protection, secure ladder placement, and careful weight distribution to avoid damage. Check your RV's roof weight rating and wear soft-soled shoes to prevent membrane punctures. For the decking replacement, you'll need a circular saw or jigsaw, drill with bits, measuring tape, and a pry bar or putty knife for removing damaged material. A moisture meter ($20-30) is invaluable for determining exactly how far the water damage extends beyond the obvious soft spot.

For the membrane work, get a sharp utility knife with plenty of extra blades, a heat gun or hair dryer for warming the rubber, and a J-roller or similar tool for pressing down the new membrane. You'll also need cleaning supplies - denatured alcohol and clean rags work well for prepping surfaces.

Material-wise, you'll need replacement decking (5/8" plywood is common, though thickness varies by manufacturer from 1/2" to 3/4"), stainless steel or galvanized exterior screws, and either Eternabond tape for patching or EPDM rubber membrane for a larger repair. For sealants, get Dicor self-leveling sealant for the final seal work and butyl tape for the new vent installation.

Step-by-Step Fix

Start by using your moisture meter to determine the full extent of water damage, then carefully cut the rubber membrane in a square or rectangular pattern around the damaged area, leaving yourself plenty of working room - at least 6 inches beyond the affected area in all directions. Use a sharp utility knife and make multiple light passes rather than trying to cut through in one go. Warm the membrane with a heat gun if it's cold and brittle.

Once you have the membrane pulled back, use your moisture meter to map out exactly how far the water damage extends. Cut out all the compromised decking, making sure to cut back to solid, dry material. Clean out any debris and let everything dry thoroughly if there's any residual moisture. Cut your replacement decking to fit snugly and secure it with exterior screws into the underlying roof structure.

For the membrane repair, you have two good options. If the damage is truly limited to a hand-sized area, you can use Eternabond tape as a permanent patch - it's incredibly durable and bonds aggressively to clean EPDM. Clean the area thoroughly with alcohol, apply the Eternabond with firm pressure using your J-roller, ensuring all edges are properly adhered.

Alternatively, since you're replacing the vent anyway, consider cutting a new piece of EPDM membrane that extends well beyond the repair area and overlaps your existing membrane by at least 6 inches on all sides. This creates a more seamless repair but requires more precision in cutting and fitting. Use EPDM contact cement or bonding adhesive for this approach (ensuring proper ventilation and following temperature requirements), and again seal all edges with Dicor self-leveling sealant.

When to Call a Pro

If you discover the damage extends more than about 2 feet in any direction, or if you find multiple soft spots during your investigation, it's time to call a professional. Large-scale roof repairs can quickly become complex, and improper installation of a large membrane section can lead to future problems that are expensive to fix.

Also consider professional help if you're not comfortable working on your RV's roof or if you discover that the underlying roof structure (not just the decking) has been compromised. Some RV service centers specialize in roof repairs and can complete this type of work for $500-800, which might be worthwhile for peace of mind, especially if your RV is still under any kind of warranty.

Finally, if you're planning to keep this RV for many more years and discover that your roof membrane is generally aging with multiple small issues, it might make more sense to invest in a complete roof membrane replacement rather than patching. A professional can assess the overall condition and help you make that decision.