Dealing with a Sagging Roof

One cursed sympton of an RV air conditioner has nothing to do with keeping cool in the heat of summer. It has everything to do with keeping dry in the rain. Our truck camper, which came to us much abused (but cheap), had a “fair” looking roof, but when the monsoons swept in with their driving rains, we found out differently. The kitchen area was awash with a steady stream of water that seemed to keep up long after the rains subsided.

Putting a little more torque on the air conditioner mounting bolts helped for a little while, but then, during a surprise spring downpour, our problems returned with a vengeance. It was time to take drastic action—replace that A/C unit roof gasket. But on closer examination, we found a bit of a “sag” under the air conditioner. While the roof itself was sound enough, we knew that just sticking a gasket in wasn’t going to cut it.

Two Schools of Fixit Thought
A sagging roof under an A/C unit isn’t all that uncommon. In some instances there are very real roof structure issues. Like things that go bump in the night, those issues can be truly frightening, with a nightmarish and expensive quality that lingers on and on. Happily, our roof was sound; it just sagged. One RV technician advised that he had found similar situations in a lot of RVs he has worked on. Happily, many of them are put right with relative ease.

There are a couple of schools of fixit thought on this matter. One says to yank up the A/C unit, replace the gasket, and add a second gasket for good measure. The other school (which we’ve subscribed to) advises that while one gasket is good, two ain’t necessarily twice as good.
In our scenario, we felt it much better to shim the roof around the air conditioner to make it level. We’ll walk you through the process.

First, some background. RV air conditioners are typically a sandwich affair. The heavy mechanical parts, including the compressor unit, are mounted above the RV roof. The mechanical portion pumps air down into the coach through a hole in the roof that is about the size of an RV roof vent hole.

Inside, under the cover of a plastic housing, a metal frame mounts up to the coach ceiling. Heavy bolts are run from the inside of the coach, through the frame, and up into the roof-level A/C unit proper. Between the outside roof deck and the bottom of the unit is (usually) a foam rubber gasket that prevents leakage of both air and water. At the “back side” of the A/C unit you’ll likely find another piece of foam rubber that allows the A/C unit to distribute its weight across the roof, to the rear of the A/C vent hole.

A Sticky Point
Removing the A/C unit isn’t always as easy at it first appears. Inside the coach, first remove the plastic housing. You’ll likely find a wiring connector that allows the A/C unit wiring harness to connect to the control unit, which is typically mounted on the plastic housing. Look it over carefully and disconnect the connector. If there is no connector but the wiring is directly connected to the controls, draw yourself a picture and note the color coding of the wires and how they connect to individual terminals.

Loosen and remove the mounting bolts that run upwards. It’s probably much faster to use an electric drill and “power wobbler” that allows you to use your drill with the appropriate socket, because you’ll likely find a LOT of threads holding those bolts in place.

With the bolts loose, go to the roof level. Carefully remove the screws or bolts that hold the air conditioner unit shroud on the A/C unit. As you may already know from bitter experience, plastic shrouds don’t take well to sunlight UV exposure and their brittle nature can cause them to disintegrate under the most cautious of handling. Do your best. I’ve found that two people working together to carefully lift the shroud off the A/C unit is best.

With the shroud removed and carefully stowed elsewhere, work at lifting the A/C unit from the roof. In our case it took repeated effort and the help of a pry bar to get the unit loose. Time and the gasket adhesive made the thing stick down with the force reminiscent of a barnacle on its favorite rock.

When you get the unit loose, you may still have the electrical supply cable attached to it. Carefully stand the unit on its side—don’t EVER turn it upside down, as frightful (and expensive) things can happen to the coolant charge if the unit is inverted. Using a scraper and plenty of patience, remove the old gasket from either the roof, the A/C unit, or both, depending on how the stick -‘em-on stuck.

Now eyeball the roofline over the vent hole. Sticking a straightedge or a piece of tight string across the vent hole and onto the surrounding roof area will soon tell you just how much your roof may have sagged. Inspect it carefully. If the roof is spongy or gives, or appears to be rotted, you’ll have to a make a call as to how to proceed. If it appears sound, just saggy, you might continue with the next phase:

Shim Shiminey—Oh, Wait—That’s a Chimney Sweep
In our case, the roof had sagged around the A/C unit area. Since we have an EPDM rubber roof, the rubber itself was folded down into the vent area, and tacked in with staples around the side of the vent in that 2-inch area between the roof level and the inside ceiling of the coach. We carefully removed the staples and worked the rubber roofing material loose. We then pulled the rubber loose at the roof top, making sure there was a clear roof deck about two inches back from all the borders of the vent hole.

Calculating the roof sag, we determined we’d need to shim anywhere between a quarter- and a half-inch to raise the A/C unit above the surrounding portion of the roof sag. A trip to the lumberyard found a “scrap” portion of 1/4-inch plywood, which we cut into 1 1/2-inch wide strips. Using those strips as shims, we encircled the roof vent hole, bringing the edges flush with the vent area. Appropriate flat top screws held the shims in place.

With shims secured, we then pulled the rubber roofing material back in place. Of course, it now “lacked” the coverage down into the “between space” where it had earlier been stapled. Using EPDM roof repair tape from the RV supply store, we carefully mended and extended the rubber roofing back to where it had been earlier.

We next installed the new foam gasket material to the bottom of the A/C unit and carefully hoisted the unit back in place. An “inside man” helped with making sure we aligned the A/C unit properly before reinstalling the mounting bolts, electrical fittings, etc.

When tightening down the mounting bolts you’ll want to be careful. The trick is to get them tight enough to keep the weather out, but not so tight you pinch the A/C unit, possibly damaging things like the squirrel cage fan. After our first attempt we found we hadn’t gone quite tight enough, as a spectacular thunderstorm and its attendant precipitation proved. Next time we’ll run the garden hose to check our work.

Just one more thing: You’ll find most RV suppliers will sell you a “universal” gasket to replace yours. Be sure to replace the old “bump strip” at the back of you’re A/C unit when you do the job.

Russ and Tiña De Maris are authors of RV Boondocking Basics—A Guide to Living Without Hookups, which covers a full range of dry camping topics. They also provide great resources in their book, Camp Hosting USA—Your Guide to State Park Volunteering. Visit www.icanrv.com for more information.