Roof Vent and Skylight Repair, in detail

Vent leaks announce themselves inside. A faint brown ring appears on the ceiling panel near a vent, or the garnish ring around a fan starts to show a dark edge, or the vinyl on the ceiling begins to lift at a corner. None of that tells you which penetration is leaking, because water above the ceiling panel runs to a low point before it stains anything.

We start inside with a moisture meter, reading a grid around the stain and outward until the readings fall off, which shows the direction water is travelling and narrows the candidate penetrations. Then the roof gets a hose test, one penetration at a time in order, with somebody underneath watching. Testing them all at once tells you the roof leaks. Testing them in order tells you where.

A fan that has stopped is not necessarily a dead fan. Fan-Tastic units have a reversible motor, a lift mechanism and on some models a rain sensor and a thermostat, and any of those can fail while the motor is fine. MaxxAir vent covers add a fixed hood over the lid, which changes both the failure pattern and the access, since the cover has to come off before anything else can.

Diagnosis is voltage at the fan, then current draw, then a look at the lift arms. A fan that hums but will not lift usually has a stripped lift gear or a bent arm from something stacked on the roof. A dead fan with good voltage at the connector is a motor. A fan with no voltage is a fuse, a switch or a corroded splice in the ceiling, and the last of those is the one owners never guess.

Shower skylights crack more than any other dome on an RV roof, and the reason is simple exposure. They are large, they are unshaded, they sit in the full ultraviolet load, and the acrylic embrittles over the years until a hailstone, a tree branch or a low branch on a campground road finishes it. The crack usually starts at a corner where the dome is fastened.

A cracked dome over a shower has a shorter grace period than most leaks, because the water lands in a wet area where a stain hides easily. Owners find these late, and by then the shower surround edge or the ceiling around the opening has usually taken water. We check the surround and the ceiling panel edge on every skylight job, not just the dome.

The job runs from inside out and then outside in. Interior garnish ring comes off first, which exposes the fasteners and the ceiling opening and lets us see whether the ceiling panel edge is sound or already soft. On the roof, lap sealant is cut and scraped off the flange perimeter, fasteners come out, and the flange is lifted clear of its bed.

What that bed looks like is the whole diagnosis. A flange that lifts to reveal a dry, intact butyl bed was not the leak. A flange that lifts off dry crumbling butyl, or worse a bed of hardened silicone somebody used as a shortcut, was. The old bed gets cleaned off the roof surface completely, down to clean membrane or fiberglass, before anything new goes down.

Two different products do two different jobs on a vent flange and confusing them is the commonest cause of a repeat leak. Butyl tape goes under the flange as the primary seal, compressed by the fasteners, and it works by staying pliable and never fully curing. Self levelling lap sealant goes over the flange perimeter and over the fastener heads as the secondary seal, and it works by flowing out and skinning.

Silicone belongs in neither position. It will not bond reliably to EPDM, it releases in sheets under thermal cycling, and it makes the next repair more expensive because it has to be removed mechanically. Anyone who finds silicone on their roof flanges has had somebody up there taking a shortcut, and the honest news is that the flange under it needs pulling and rebedding rather than resealing.

Owners frequently ask for a lid, because the lid is the broken visible thing. Fitting a lid to an existing flange is genuinely quick and genuinely cheap, and when the flange bed is sound it is the correct repair. When the flange bed is the actual problem, a new lid changes nothing except which part looks new. The water keeps entering under the flange exactly the way it did before, and now it does so behind something shiny.

We pull the flange on any vent that has produced an interior stain, and we do not offer a lid only repair on one that has. That is a position that occasionally costs us the job, since another shop will fit a lid for less. The coach comes back the following winter with the same stain and a larger soft area, and the second repair costs more than the first would have.

This is the least expensive category of roof work we do, and the smallest jobs land at the very bottom of the band. A vent lid on a sound flange, a fan motor on an accessible ceiling, a single skylight dome swap on a roof with no other issues, all of these are one to two hour jobs plus parts, with body supplies at $5 per body hour and any hazmat handling at $45 flat where it applies.

The limit is that a small number only survives if nothing else is wrong. Every vent job here includes a walk of the surrounding penetrations, because a coach with one flange leaking at ten years old typically has three more within a season of doing the same. Fixing one and ignoring the others is how an owner ends up paying access and setup costs four separate times.