RV Roof Leak Around a Skylight

A leaking RV skylight has two possible causes: the plastic dome has cracked, or the sealant around its frame has failed. Both are common, because a skylight is a big hole in the roof covered by plastic that sits in the sun for years. Caught early, either one is a small job.

How do you know if an RV skylight dome is cracked?

Skylight domes are acrylic or polycarbonate, and UV is their whole life story. They yellow, they fog, and eventually they go brittle, and then a hailstone, a dropped branch, or one winter’s snow load finishes the job. Cracks usually start small and spread out from the mounting screws, where the stress is. From inside, a failing dome shows heavy yellowing or a spiderweb glint when the sun hits it. From the roof, look closely around every screw head. If you’re not sure, a clear photo of the dome from the roof is usually enough for us to tell.

One caution before you blame the dome: many bathroom skylights have two layers, and condensation between them after a shower is common and harmless. Moisture that comes and goes with steam is a ventilation issue. Drips that arrive with rain are a leak.

Is the sealant around the skylight failing?

The dome sits on a flange screwed through the roof, bedded on butyl tape, with lap sealant over the screws and edges. Water gets past the frame in one of two ways. The lap sealant on top cracks and lifts with age, or the butyl tape underneath dries out. If it’s the butyl, fresh caulk on top won’t fix it: the frame has to come up and be re-bedded. One clue: if the sealant looks intact but the garnish ring inside stains after rain, dried butyl is the likely cause.

Should you repair or replace a leaking RV skylight?

• 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 one-season fix at best. Caulk on flexing, brittle plastic splits again, usually where you can’t see it
• Failed lap sealant: remove the old bead fully and reseal. Bead-over-bead inherits every crack underneath
• Dried butyl: lift, clean, re-bed, and reseal. Half an hour of doing it right beats caulking it every year

How serious is a leaking RV skylight?

A skylight leak drops water straight into a bathroom ceiling, usually the thinnest, dampest panel in the RV, with a vent fan’s wiring nearby. 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 what an inspection is for.