RV Roof Leak Around a Skylight

Cut a big hole in a roof, cover it with a piece of plastic, and park the whole thing in the sun for ten years. Described that way, it’s no mystery why skylights sit at the top of the leak-point list. The good news: skylight leaks are cheap to fix early and easy to diagnose — once you know it’s really two separate suspects.

Suspect one: the dome

Skylight domes are acrylic or polycarbonate, and UV is their whole life story. They yellow, they fog, and eventually they go brittle — at which point a hailstone, a dropped branch, or one winter’s snow load finishes the job. The cracks usually start small and radiate from the mounting screws, where stress concentrates. From inside, a dome on its way out shows as heavy yellowing or a spiderweb glint when the sun hits it; from the roof, look closely around every screw head.

One caution before you blame the dome: many bathroom skylights are double-layered, and condensation between the inner and outer dome after a shower is common and harmless. Moisture trapped between layers that comes and goes with steam is a ventilation story. Drips that arrive with rain are a leak.

Suspect two: the flange

The dome sits on a flange screwed through the roof, bedded on butyl tape, with lap sealant dressed over the screws and edges. Two ways in: the lap sealant on top cracks and lifts with age like it does everywhere else on the roof — or the butyl underneath has dried out and lost its squeeze, in which case fresh caulk on top is cosmetic. If the sealant looks intact but the garnish ring inside shows staining after rain, dried butyl is the likely story, and the fix is lifting the flange and re-bedding it properly, not another bead.

Repair or replace?

• Cracked dome: replace it. Domes are an inexpensive part; measure the rough opening because sizes vary more than you’d expect
• Yellowed and brittle but not yet cracked: plan the replacement on your schedule, before the weather picks the date for you
• Cracked dome, caulked over: a season-long fix at best — caulk on flexing brittle plastic re-splits, usually in a spot you can’t see
• Failed lap sealant: remove the old bead fully and reseal; bead-over-bead inherits every crack underneath
• Dried butyl: lift, clean, re-bed, reseal — half an hour of doing it right beats an annual caulking ritual

Worth taking seriously early

A skylight leak drops water straight into a bathroom ceiling that’s usually the thinnest, dampest panel in the RV, with a vent fan’s wiring nearby for company. Caught at the “slight stain on the garnish ring” stage, it’s one of the smallest jobs we do. Caught two seasons later, the skylight is the cheap part of the invoice. If you’re not sure which stage yours is at, that’s exactly what an inspection is for.