RV Roof Vent and Skylight Repair Done Right the First Time

Why Acrylic Domes Crack in Southern California Sun

Vent domes are acrylic or polypropylene, and both age the same way here. UV breaks down the polymer from the outside in. The surface goes chalky, then hairline crazing appears, then the material loses impact strength until a dropped branch, a hail stone, or simply a hot day followed by a cold night puts a crack straight through it. Ten years is a long life for a dome parked outside in this climate.

Smoke tinted and white domes generally outlast clear ones, because the pigment blocks a share of the UV before it reaches the polymer. A clear dome over a bathroom looks good for about five years and then starts crazing. If you park outside year round and you want the daylight, plan on replacing clear domes on a schedule instead of waiting for the failure to announce itself.

The crack itself is not the emergency. The problem is that a cracked dome flexes, and a flexing dome works the hinge, the hinge works the flange, and water starts tracking under the lid onto the vent collar. That is the whole path from a thirty dollar part to a wet ceiling, and in a normal winter it takes one season to travel.

Powered Fan Failures and What Actually Broke

Powered roof vents fail in a small number of predictable ways. The motor bearing dries out and the fan gets loud before it gets slow. The lift arm gearbox strips, usually on the plastic gear, and the lid stops opening. The rain sensor board corrodes and the lid cycles on its own at odd hours. The thermostat sticks closed and the fan runs until the house battery is flat.

Diagnosis is straightforward. We check voltage at the fan with the switch on, check the ground, then check motor draw. A fan reading full voltage and drawing nothing has an open motor. A fan drawing high current and turning slowly has a seized bearing. A fan with good voltage and a healthy motor but a dead lid has a gearbox or lift arm problem, which is often a separate and much cheaper part.

Whether we replace the motor or the whole unit comes down to age and parts availability. On a unit under about five years old from a current model line, motor and gear kits are available and the repair is worth doing. On an older discontinued unit, the labor spent chasing parts exceeds the price of a new assembly, and we will say so before we start hunting.

• Loud fan that later gets slow: motor bearing is going
• Lid will not open or close: lift arm or gearbox
• Lid cycling on its own: rain sensor or control board
• Fan runs and will not shut off: thermostat or switch
• Full voltage with no current draw: open motor winding

Hinges, Lift Arms, and Lids That Will Not Stay Closed

Vent lid hinges are the most overlooked failure on an RV roof. On most designs the hinge is a plastic pin through a thin plastic ear molded into the lid. UV embrittles the ear, road vibration works it back and forth, and one day the lid lifts at speed and folds back or departs entirely. Now the vent is open to the sky and you find out at the next rain.

The intermediate failure is worse than the total one, because you do not notice it. A hinge with one broken ear lets the lid sit crooked. Crooked means the gasket only contacts on one side. Water runs in every time it rains and evaporates before you look, until one day it does not. If you can rock a closed lid with your hand, the hinge is finished and the gasket is not sealing.

Hinge kits are inexpensive and the repair is quick. Where it gets costly is when the lid has already departed and taken part of the base with it, or when the sun has cooked the base flange enough that it cracks the moment you back out the old screws. We check base condition before quoting a lid, not after the old one is off.

Garnish Rings and the First Sign of Water Inside

The garnish ring is the interior trim ring covering the raw opening in the ceiling. It is the first thing that shows you have a vent leak, because water tracking down the vent collar hits the ring and wicks into the edge of the ceiling panel. A brown crescent on the ring, or a ring that has gone from white to yellow on one side only, is not cosmetic aging. It is a report on what is happening above it.

Owners often wipe the stain and forget about it. The next stage is the ceiling panel around the ring going soft, then the vinyl ceiling fabric releasing and sagging, then the ceiling luan turning dark and losing fastener hold. At that point the repair includes a section of ceiling panel, and the price moves from a couple hundred dollars into four figures.

When we pull a stained ring, we meter the ceiling panel edge before anything goes back together. If the panel reads wet, resealing the vent alone leaves trapped moisture sitting in the ceiling. That gets opened, dried, and verified before the new ring goes on. It adds hours to the ticket, and it is the difference between a repair and a delay.

• Brown or yellow staining on one side of the ring
• Ring that has loosened or will not sit flat
• Soft or spongy ceiling panel at the opening edge
• Vinyl ceiling fabric releasing near the vent
• Musty smell when the vent is opened after rain

Butyl Under the Flange, Self Leveling Sealant on Top

There are two sealants on a correctly installed vent and they do different jobs. Butyl tape goes under the mounting flange as the primary seal. It never fully cures, it stays plastic, and it is what actually keeps water out of the opening. Self leveling lap sealant goes on top of the flange and over the screw heads as the secondary seal that protects the butyl from UV and mechanical damage.

Most failed vents we open were installed with lap sealant only, or with silicone, which is the worst possible choice on an RV roof because nothing bonds to cured silicone, including fresh silicone. Removing a silicone repair adds an hour of scraping and solvent work before we can even begin doing the job the correct way, and that hour goes on your ticket.

Technique matters as much as material. Old butyl comes off completely, down to clean substrate. Screws go into sound decking, not into stripped holes, and a stripped hole gets a larger fastener or a backing repair. Flange screws get snugged in a cross pattern until the butyl squeezes out evenly all the way around, then lap sealant goes on in one continuous bead rather than dabbed over each screw head.

• Butyl tape under the flange as the primary water seal
• Self leveling lap sealant on top for UV and mechanical protection
• No silicone anywhere on an RV roof, ever
• Old sealant removed completely before new material goes down
• Screws snugged in a cross pattern for even butyl squeeze out
• Sealant matched to the roof material, EPDM, TPO, or fiberglass

Skylights Over a Shower Pan

A skylight over a shower pan lives a harder life than any other opening on the roof. It takes the same UV as everything else, plus steam and heat cycling from the inside every time someone showers. The acrylic goes brittle and the inner dome crazes, and the sealant around the flange sees more expansion and contraction than any other bead on the roof.

It is also the worst place on the coach to have a leak. Water coming through a shower skylight runs down the inside of the surround, behind the shower wall, and into the floor at the pan edge, which is already the most common soft floor location in any RV. By the time it shows on the floor you are looking at pan removal and decking work, not a skylight job.

We treat shower skylights as an annual inspection item rather than a fix it when it breaks item. Checking the dome for crazing and the sealant bead for cracking takes ten minutes while we are already on the roof for something else. Replacing the dome is usually under an hour. Rebuilding a shower surround and the floor underneath it is a week in the bay.

Sizing Standards, Fitment, and What a Delay Really Costs

RV roof openings are standardized more than owners expect. The common vent is a 14 by 14 inch rough opening, which is why most lids, fans, and covers interchange across brands. Skylights are far less standardized and are usually specified by the outer flange dimension and the dome rise, so a measurement of the opening alone is not enough information to order the correct part.

When we quote a skylight we need flange length and width, opening size, and dome height, and on older units we want a photo of the mounting flange because some are molded into the surround rather than bolted to it. Getting that right up front is why a skylight sometimes takes two days when a vent lid takes an hour.

Pricing runs on four rules. Body labor is $210 per hour, parts at or under $100 carry 100 percent markup, parts over $100 carry 35 percent, and the 7.75 percent tax applies to parts and materials only. A dome only replacement is about 0.75 hours, or $157.50, with a $42 dome at $84 and $18 of sealant at $36, plus $9.30 in tax, for $286.80 out the door.

A powered fan replacement with a full reseal is about 2 hours at $210, or $420, with a $265 fan assembly at $357.75, butyl at $44 and lap sealant at $68, plus $36.41 tax, landing at $926.16. Now the delayed version. A shower skylight plus a section of stained ceiling panel runs around 9 hours, or $1,890, with roughly $796.50 in marked up parts and $61.73 in tax, for $2,748.23. That one crosses $2,000, so it takes a 50 percent deposit of $1,374.12 to start.

• Standard vent rough opening is 14 by 14 inches
• Skylights ordered by flange size, opening size, and dome rise
• Body labor billed at $210 per hour
• Parts at or under $100 marked up 100 percent, over $100 marked up 35 percent
• Sales tax of 7.75 percent applies to parts and materials, not labor
• Jobs above $2,000 take a 50 percent deposit before parts are ordered