Monday, December 4, 2023


RV ‘Gremlins’, Part 6: The final chapter—RV water leaks

I saved the best for last! Sadly, everyone who owns an RV will experience a water leak at some point. The RV “gremlin” hiding here is figuring out why the area you find a water leak in your RV isn’t the area where the water is actually coming from. It can be baffling!

Once you see the signs of a water leak inside your RV it’s typically already caused damage along the way.

It is very hard to find the actual entry point since water can enter several areas in an RV and will “travel” through hollow tubing in the framework and even between layers in the sidewall. Take a look at the artwork below of the Winnebago product:

RV water leaks: Clearance lights

Clearance lights are notorious for allowing water in with a cracked lens or poor sealant between the base and the cap. That water makes its way to the overhead bulkhead, travels to the A-pillar, and then down to the door frame or floor to the sidewall joint. It can start delamination of the sidewall or even come out of a compartment. So you take it into the dealership or you try to seal it yourself and coat all the compartment seams with silicone or even “Flex Seal” and it doesn’t leak for six months. Then all of a sudden it does again! Unless you can recreate the exact circumstances of weather and moisture penetration, it probably won’t go into the clearance lights, especially if you are not driving into pouring rain and you think it’s fixed.

Most manufacturers simply drill a hole in the fiberglass cap on both motorized RVs and trailers, run the wires through the hole, and install the clearance light housing. Typically, the housing has a rubber gasket or the manufacturer applies sealant around the edge. But that can dry up and crack or the lens can crack. Or if you pull off the lens to replace a bulb, there is a moisture leak potential. With all of these, that hole is a funnel for moisture to fill the overhead and either run down the side frame or even back (in the case of high-mounted lights). Make sure all your clearance lights are sealed front, back, and even on the sides.

RV water leaks: The roof

The roof of your rig has a number of potential moisture penetration points starting with the front cap to the roof seam. Typically, your front cap is either a hard fiberglass cap or a fiberglass sheet. Both meet the roof material with what we call a “J” trim. As temperature changes throughout the day, materials will expand and contract at different rates. If you have a rubber membrane, it will expand more than the hard fiberglass, which makes it difficult for the manufacturer to keep this seam sealed. The “J” trim has the material overlapping inside the aluminum curve of the “J” so it can move back and forth. So the sealant used there must move with it without breaking the seal. Sealants dry up, so it is important to check all the seams and sealant a few times a year.

Moisture can penetrate into this seam and travel around the sides and follow the hollow tubes and come out in the bedroom closet! Or, if there is a hole in the tubing, it will come out somewhere down the sidewall between the layers and cause delamination, which is loose material and looks like bubbling or large gaps. The Gremlin here is not only finding the entry point or points, but also replicating the conditions in which the leak occurred.

I have talked with owners that have taken their unit in 4-5 times to have a leak fixed in the bedroom or up front, only to bring the unit back home and have it happen again. The dealer brings the unit into the completely level service bay, soaks the unit down with a garden hose, and doesn’t find a leak, or finds a small one. They seal the back cap, sidewall to roof joint, or shower vent and test it again… no leak. You bring the unit back home, park it in the driveway or other storage location that has a slight decline, and the next time it rains, you have another leak. Frustrating!

The importance of visual inspection and maintenance

Out of sight, out of mind. That’s what usually happens with the typical RV owner since we don’t get up on the roof very often and take for granted the windows and compartments are similar to a car. They are not, and we need to visually inspect them at least once a year.

Unlike a car that has a welded unibody construction and solid engineered components, your RV has wood, fiberglass, rubber, and other materials similar to a home that you periodically inspect and reseal. Plus, we let our RVs bake in the sun when not in use, and temps can get over 100 degrees inside. We also let them sit in sub-freezing temperatures. And, as stated before, all materials expand and contract with temperature changes and sealants can fail.

Key areas to inspect for RV water leaks are

  • Roof to sidewall joint
  • Anything mounted to the roof such as vents, antennas, skylights
  • Back cap to roof
  • Front cap to roof
  • Window seal, which is usually a butyl (putty-like) tape
  • Slide out seal/gasket
  • Sidewall to floor seam
  • Compartment gaskets
  • Compartment interior seams
  • Door gasket
  • Roof air conditioner gasket

Roof air conditioner gasket

The roof air conditioner gasket is an area that most RV owners know nothing about. Most roof air units have a foam gasket between the unit and the roof that is compressed corner bolts. Some models require these bolts to be re-torqued every year as the gasket compresses and needs to be tightened to keep it sealed. Here is a photo of a unit that did not have the procedure done. By the time the leak was found inside, the damage was already done. This trailer needed a new roof, which was $8,000 for parts only. The unit was only valued at $6,000!

Check the owner’s manual for your brand of air conditioner to see if it has this recommendation. I don’t typically worry about the actual torque setting. Just do a yearly hand-tightening, which is sufficient.

The best method to find the RV leak “gremlin”

The old way to find leaks in an RV has been to soak the unit down and go inside with a flashlight and look for the water to pour out. Since you cannot recreate the angle of the unit, the driving rain, or other components, it becomes a hit-and-miss approach.

The absolute best approach to finding a leak in an RV is to use the Sealtech product, which draws air inside the rig from a roof vent or side window and pressurizes the unit. Then spray the outside with soapy water and you will find the leak.

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook.”

More RV “gremlins”

Read more from Dave here



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Solar Steve (@guest_195831)
1 year ago

B ack some years, on a small class C, I had water leak around a rear window. Had the window re-set, but still leaked. This RV had a fiberglass roof that included the top 1 foot of walls. The joint was covered with a metal strip with a rubber “half tube” all the way around the rig. At one campground I saw the leak again, and lifted the rubber tube seal at its end point. Water poured out from behind the rubber strip. I removed the rest of it, all the way around the aluminum bracket that joined the fiberglass side walls and top piece. The rubber trim was to cover the screws in that aluminum bracket strip that ringed the fiberglass body. Aha, one screw was entirely missing, and it was a foot above that window where the leak showed up. I replaced it and then used 3M marine seal to fill over the screws rather than the hollow rubber tube.

Jesse Crouse (@guest_195491)
1 year ago

Pressure test, pressure test and pressure test. How do I know? The hard way- had it done and no more leak.

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