TLDR
Coastal UV degrades lap sealant faster than manufacturer intervals assume. Inspect twice a year and reseal penetrations every one to two years, not every five.
RVs stored near the coast need roof sealant inspection twice yearly and penetration resealing every one to two years. Manufacturer intervals assume moderate UV exposure, and constant coastal sun degrades lap sealant considerably faster.
The Interval Problem
Manufacturer maintenance schedules are written for an average. That average includes coaches stored in garages in temperate states, and it produces a resealing interval that is genuinely reasonable for those vehicles. It is not reasonable for a coach sitting uncovered within a few miles of the Newport Beach coast.
Two mechanisms are working at once here. Ultraviolet exposure breaks down the plasticisers in lap sealant, which is why it shrinks, hardens, and eventually splits. Salt in the air attacks the fasteners and terminal bars holding the membrane down, and works into any gap the shrinking sealant opens. Neither is dramatic. Together they turn a maintained roof into a leaking one in about a third of the time an owner expects.
What the Failure Actually Looks Like
- Year one to two: sealant begins to lose flexibility. Nothing visible unless you are looking closely at penetrations.
- Year two to three: hairline shrinkage cracks appear at the edges of vents, skylights, and air conditioner mounts.
- Year three to four: water begins entering intermittently during rain. Nothing shows inside yet because it is tracking along the decking.
- Year four to five: a ceiling stain appears, frequently several feet from where the water is actually entering.
- By the time you see the stain: decking is soft, and in many cases the subfloor below has already started.
The Cost Difference
| Caught at | Typical repair | Cost |
|---|---|---|
| Sealant shrinkage, no intrusion | Reseal penetrations | $750 to $2,000 |
| Intrusion, membrane sound | Reseal plus targeted membrane repair | $1,500 to $4,500 |
| Decking soft, localised | Partial decking and membrane replacement | $4,000 to $9,000 |
| Decking and subfloor compromised | Full roof replacement plus interior | $15,000 to $40,000 plus |
What to Actually Do
- Inspect twice a year, spring and autumn. Photograph every penetration so you can compare against last time.
- Reseal penetrations every one to two years rather than waiting for visible failure.
- Look specifically at air conditioner mounts, vent flanges, skylight edges, antenna bases, and the front and rear terminal bars.
- Cover the vehicle if it is stored long term and covering is practical. It roughly doubles sealant life.
- Consider a coating on the roof and body. It does not replace sealant maintenance but it slows the surrounding degradation.