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RV Doctor ColumnRV Doctor #278 Dear RV Doctor, My RV roof leaks in several places and the roof sagged around the air conditioner. While surveying the damage I determined that the roof is constructed in layers including rubber material, plywood and foam. The air conditioner mounts to a 2' x 6' piece of plywood that is supported only on one end; like a diving board. I think I need to replace all but the foam and some of the rafters. Can you offer advice on the best way to proceed for a do-it-yourselfer? Roy Avery, (Harrisburg, PA) Roy, Extensive damage from water leaks usually mandates a complete roof replacement; a major repair best left to the professionals. If, however, you are quite handy with tools and you can provide a covered area to work and you have some spare time on your hands, it will save a lot of money if you decide to attempt it yourself. First remove every component from the entire roof area, A/C, all vents, antenna, running lights, storage pods, racks, ladders, etc. All the side trim, awning rail, drip molding, etc., will also have to be carefully removed. Typically the rubber membrane is cemented to the plywood substrate and folded over the sides of the RV and stapled prior to the trim pieces being attached. At the front and back there may be a flat molding strip or the membrane might simply tuck under a fiberglass cap. Remove all the rubber membrane and locate the damaged plywood sections. If there are many, simply remove them all to inspect the inside of the roof. In some cases, the water may have permeated the foam insulation and possibly the interior ceiling paneling. Replace all damaged or warped wood rafters with new. Gradually taper the rafters to the ends so that they are thicker in the center. In other words, create a slightly crowned roof. This will eliminate low areas and ensure proper water drainage, especially at that sunken air conditioner location. Once all the new insulation and rafters are secured, cover the entire roof with new plywood. In some cases I recommend 3/8-inch plywood, though 1/4-inch will usually suffice. Take care to make tight seams between the panels. Be sure no screws or staples are sticking up above the level of the plywood. Pay close attention to the seams. They must remain flush and smooth so the EPDM rubber will not tear or crease during installation. Likewise, bevel the edges of the plywood slightly at the sides of the roof. This whole preparation stage is crucial! If the cement is a bonding-type, such as contact cement, it must be applied to the bottom ply of the EPDM as well as the plywood substrate. When a water based adhesive or pressure sensitive cement is used, it is applied only to the plywood. Purchase enough EPDM rubber so it can be rolled out the entire length of the RV. It should also extend over the sides of the RV; enough to fold down behind the drip molding or awning rail. Fold back the membrane front to rear about halfway and apply the cement by brush, roller or spray gun. If you use solvent-based contact cement, apply it to both the substrate and the membrane and allow it to dry. If you are supplied with a water-based, pressure sensitive adhesive, apply the membrane while the cement is still wet. Roll out all air pockets from the centerline of the coach to the sides with a lightweight roller or a push-type broom. At the RV sides, fold the material over the edge of the roof and staple it to the sidewall on top of the siding material. Apply butyl tape or caulking to the back of a drip channel or awning rail prior to reinstalling it to the sides of the RV. Excess material hanging below the molding or rail is simply trimmed off with a razor knife. After the roof is completely cemented in place and secured around the perimeter, cut all the openings for the sewer vents, the refrigerator vent, the 14-inch vents, the roof air conditioner opening etc., with a sharp pair of scissors. When cutting the openings, always radius the corners to eliminate the possibility of the EPDM tearing. If possible, have excess rubber fold into the opening and staple it to the sides of the opening. Apply butyl tape and install the vents as usual and seal all screws, flanges and edges with the appropriate lap sealant. When working with EPDM rubber and lap sealant, do not smooth out the bead of sealant after application. Above all, take your time. Dear Gary, I have a 1985 Wilderness and the bathtub will not drain properly until I open the sewer valve on the outside of the trailer. Does that mean I may have a vacuum problem with the air vent? Jerry Spencer, (Topeka, KS) Jerry, Chances are the vent has fallen into the tank below the surface of the liquid in that tank - with no place for the air to escape, the tub barely drains. When you open the termination valve, air actually rushes in which aids in the draining of the tub. It is usually necessary to drop the tank to properly affix the vent pipe to the tank so this may be a task for a pro. But first, be sure it has fallen. Remove the vent cap on the roof for that tank; many have caps that twist off. If the 1-1/2" ABS drain pipe is not sticking up above the roof line about one to two inches, then it has fallen into the tank. Here's a brief overview of how it's done should you want to tackle this yourself. Drain and flush both holding tanks. Disconnect the termination assembly so that the gray water tank can be dropped straight down. Remove the panel below the tub and disconnect the "P" trap and the upper portion of the drain line. Locate the suspect vent pipe inside a closet or lavatory cabinet. Hack saw the vent pipe as close to the floor as possible. Use a flashlight and a mirror to view the top of the tank from under the chassis and look for any other drains or vents that may enter the top of that tank. All drain pipes must be cut as close to the floor as possible. Remove any electrical wires attached to "well nuts," or probes that connect the monitor panel to the tank. Be sure to mark the exact location for any such wires and to note their respective colors. Locate and determine just how the tank is secured to the underside of the RV. Many installations utilize mounting straps or metal bands that completely support the bottom of the tank. Some may have an upper flange that is bolted or screwed to the underside of the coach. Look over the installation carefully to determine which method was used. Support the tank with a floor jack and remove all the supporting hardware and carefully lower the tank to the ground. If the existing fitting for the vent pipe is damaged or if a rubber grommet fitting has been used, install a new fitting which will allow you to insert the vent tube into the fitting yet prohibit further movement down into the tank. Reinstall all components and the tank in the reverse order and insert a length of ABS pipe into the new fitting on top of the tank. You can use a new full-length section or use two shorter pieces and connect them with an ABS coupler somewhere convenient under a cabinet or inside a closet. Fill the tank completely with fresh water to test for leaks anywhere in the system. And don't forget to reinstall and seal the vent cap up on the roof. Dear Gary, Do you have a source for mud dauber or wasp screens for the furnace inlet and outlet vent? Bill Knapp, (Broken Arrow, OK) Bill, I do not recommend blocking the fresh air inlet tube or the hot exhaust tube on the RV furnace at all. Any air restriction on these pipes will cause erratic appliance operation and shorten the life of the appliance. I do, however, recommend taping off those openings during winterizing or other periods of storage or non-use to keep the critters out, but during actual RV use you do not want to modify or impair air flow in or out of the unit. All mud dauber's nests should be checked for and routinely removed during the annual cleaning of the furnace.
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