Your RV’s rubber roof thinner than a dime; damage could cost you $10,000 to fix

If you have a rubber roof, then your beloved home-on-wheels is being protected by a flexible plastic sheet that is thinner than a dime. For reference, a dime is 53 mils thick; an RV roof membrane is 27-45 mils. You don’t need to be a math whiz to see that 27 << 53! [<< means “much less than,” in layman’s terms]

This membrane, whether EPDM, TPO, or PVC, can be punctured by tree branches, large hail, garage doors, and hard-soled shoes. Your roof sealants can also crumble or peel with age, leaving your seams and cutouts defenseless from water intrusion. If your roof decking repeatedly wets and dries, the wooden decking will crumble. Unfortunately, you may not realize this is happening until your ceiling panels begin to bubble, too.

Often, that’s when you call me, your RV service technician (in my case, also a former RV design engineer)—and I have the unfortunate responsibility of informing you that fixing that RV roof soft spot might cost you $10,000.

But perhaps I can save you the headache in the first place.

The origin story of your RV roof “soft spot”

While there’s no such thing as a standardized RV roof design, the most common RV roof construction is 3/8” thick OSB 4×8 sheets fastened to wooden (sometimes aluminum) trusses spaced 16” or 24” on center. Some “ultralight” RVs may use foam-cored sandwich panels made with 1/8” or 1/4” plywood skins instead of OSB decking, and if the sandwich panel is thick enough, the trusses can be eliminated entirely. However your roof is constructed, it’s probable that some wood, somewhere, is responsible for its integrity.

Don’t hate on wood. It’s a resilient, strong, eco-friendly, water-resistant building material. It naturally absorbs and releases large amounts of water vapor, just like a sponge. But wood doesn’t like saturation cycles: wet, dry, wet, dry, ad nauseam. When wood contains more than 20% moisture by weight, two things happen: (1) Mold can grow. (2) Wood naturally loses some rigidity (think of bendy green wood saplings).

And in the case of OSB, a manufactured wood product, the damage from wetting is even worse. The individual chips swell, destroying the interstitial glue bonds. The panel self-destructs, returning to the chopped-up wooden flakes from whence it came. You will notice this self-annihilation as a “soft spot” that tries to swallow you up when you step on it.

It doesn’t take much water to start the saturation cycle. I actually say the smallest holes are the most dangerous. You don’t notice anything until the roof gives way! That’s why bi-annual roof inspections are so important. Look for rips or tears from scraping tree branches, pinholes from rocks stuck to the bottom of your shoes, or even micro-cracks from protruding screw heads that were missed at the factory. Inspect the roof sealants for any peeling or flaking. Personally, I always wear soft-soled shoes or just socks when walking on a rubber RV roof to prevent any further damage.

So, if you’ve found a soft spot in your roof, how do you fix it?

Option 1: Get a new roof—Lock, stock and barrel

Here’s the bad news: For most RVs, the only way to fix a soft spot in your roof—and to replace any rotted wood framing or molding insulation—is get a new roof. The whole shebang. Remove every roof component and every piece of trim, tear off the old membrane, replace the insulation, sister* new trusses, re-deck, maybe overlay, roll on a new membrane, and do everything else in reverse. [*The term “sister” means to attach a similar or identical-sized piece wood, etc. to the existing truss.]

It’s a burly job. It will gobble up dozens, may even hundreds of hours. It demands meticulous craftsmanship, two or three ladders, and a shop’s worth of tools. Hence, why the commercial cost to replace an RV roof ranges from $150 to $350 per linear foot.

Option 2: Patch ‘n’ pray!

Your second option is to patch the damaged area. You can try this if the soft spot is rather small, towards the center of your roof, and you can’t detect any other damage (swelling seams, soft spot, lumpy decking) on the rest of the roof.

1. Outline the affected area in a rectangle and add another 2+ feet on all sides, ending on the center of a truss if possible.
2. Cut out and peel off the roof membrane.
3. Remove and replace any affected decking and insulation in the area.
4. Reframe what’s necessary. Add edge blocking for the OSB patch.
5. Install a new membrane. Seal the seams with lap sealant and repair tape.
6. Pray hard, pray often.

As a service technician, I rarely offer this option. I am willing to consider a patch job if the roof membrane is in great shape and just recently damaged, but once I see signs of water damage, I don’t offer patch jobs. A soft spot may be small, but until you peel off the membrane, it’s hard to estimate the extent of the unseen damage. There’s too much that can go wrong.

Option 3: Live and let live

Let me ask the uncomfortable question: Does an RV roof soft spot actually need to be fixed?

Yes? No? Maybe?

You see, many (most?) RVs have hidden water damage. Somewhere, you probably have a soft spot on your roof, a leaky fitting behind your shower, a dry-rotted patch of subfloor, or some stained carpet in the corner of your slide-out room. I see so much water damage that I’ve become dispassionate and fatalistic to a flaw. RVs don’t shed water as they should.

So Option 3 is to … leave it alone. Use it. Sell it. Trade it in.

I know, I know. It’s a horrible option. No one likes the idea of living underneath a damaged roof—and there could be mold in your ceiling! Gross!

(BTW—If you do find water or mold anywhere in your camper, you need to run a dehumidifier for at least a week to draw out water vapor until your structure has less than 20% moisture content. Keep the camper indoors, if possible, and keep all the windows closed.)

I’m not advocating this option, per se. But I am aware that RV depreciation is a [CENSORED]. Within about 5 years, your RV is worth about half what you paid for it. And while some people live in their rigs full-time, others take out their campers only twice a year. At what point does it make more sense to trade it in for a new(er) RV with a shiny, spotless roof?

Conclusion

If you find a soft spot on your RV roof, you have three options: Live and let live; patch and pray; or pay for a new roof. It’s a decision no one wants to make. So inspect your RV roof at least twice a year, keep those sealants fresh, and stop those soft spots from happening in the first place!

More from Ross, the RV Engineer.

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