Arched steel roof rafters

[lockman]

Sent: 7/22/2004 12:53 PM

Hi WannaWinne. Our 78 D23 has a one piece alum. roof with fiberglass end caps. When we bought it we gave the roof a through exam and were convinced the roof was sound. It looked great. Leaks must be A/C and vents and seams. WRONG. All of the really bad damage was caused by the plumbing vent pipes. They were sealed using plastic volcano shaped cones. I do not think these were factory, they were too poorly done. The cones were made multi sized for 1" and 1 1/2" pipe. The installer roughed the opening with a file and forced it on. The pressure of being too tight caused both to split full length leaving a big gap for water to enter. It did, big time. All of the other water damage was done due to unseen pin hole leaks. Seams and other openings were all dry. We found our first pin holes when removing the glue residue from the inside of the roof alum.and hundreds more when cleaning the top side with grinders equiped with wire wheels. We put three coats of white rubber roof coating to perminently seal. I now believe that if its old and bare metal, it will have holes. Wether these are caused by the glue from the inside or the acidic bird or tree dropping outside I don't know. As to the steel rafters. We had planned on using just 1" marine grade plywood cut into strips as our rafters. I was concerned about bowing due to the weight of the A/C unit. My brother in law suggested metal rafters being the machinist/millwright type. I quickly agreed as it was now his problem not mine. A few days later two metal rafters showed up. Now I am sure he will take all the credit for a great design but, but it was more dumb luck and scrap metal that made them so perfect. Sorry I do have pictures but no sanner to post them yet. I will do my best to describe. They started life as approx. 8 ft. x 8", 12 to 14 guage flat metal stock. They were bent to have a "U" shape in the middle, but with a flat top, not rounded and flat legs on each side. Sort of an inverted letter U with legs out it sides so it stand up on its own. The only important measurement was the height was exactly 1" from the top outside surface to the bottom outside surface. That way it was the same height as our other wood rafters and foam.We did not use thin plywood, we bonded rafters and foam directly to the inside of the alum. roof. We are never on the roof expect for repairs and we use padded walking boards to spread our wieght out. As for the arches. I suggested it would have been nice to have an bend in the rafters so when the weight of the A/C was put on them they would bend flat instead of down. He gave me one of those " is this suposed to be a problem look" and promptly laid  it on the work bench and suppored the inverted rafter on each end with 1/2 inch plywood blocks. Pushing  down hard in the middle gave it a half inch bend. We had planned on filling the channel of the rafter with a wood strip to give us a glue and nail surface for the luan panelling. By applying HD construction adhiesive to the 8 ft long filler strip and rafter and using a C clamp in the middle of the piece we had a radius. 1/4" pylwood  spacers were placed between the center and the ends and C clamped there and finally clamps at each end. Left to cure for a day or so we now had curved metal rafters with wood strips inside. I know they support at least 250 pounds with out bending probaly a lot more. The adhiesive was like liquid nails, but on steriods, it supposed to be perminent. I have to go to work now so I will cover installation tonight. Mike       

[54PrairieSchooner]

Sent: 7/22/2004 6:13 PM

Mike, thanks..I read thru this once and will let it soak in (no pun intended) and reread...I got most of it from your verbal but the wood strip part inside the metal rafters is more detailed...I'll review again later on tonight....

[lockman]

Sent: 7/24/2004 3:21 AM

Hi WannaWinne. A quick clarifiacation, my brother in law tells me that nothing I could ever due would bend his rafters. They only had some minor "flex" in them, 1/2 " over 8 feet is minor and we did use clamps to accomplish this. The rafters were made to be installed with the open part of the channel facing down, and the flat legs out each side, resting on top of the steel angle iron rails running down each side of the coach. The flat top surface of the inverted "U" shape channel was for supporting the alum. roof. We used HD adhesieve to bond the inside of the alum. roof  to the top of the steel rafter. This way we got  a very strong bond and yet the two different metals never actually touched each other. The flat side legs were bolted thru the angle iron rails at each end. Oringinally the rafters were to be left empty in the channel, but as it turned out we were going to need to  join two sheets of luan right in the middle of one of our rafters. Hence the idea for filling the channel with wood to provide a nailing surface for one and a glue surface on the other rafter. The wood filler strips was cut to fit inside the channel and be flush with the legs to keep it to our 1" height requirement. The filler strip also became the key to putting our 1/2" arch in the rafter. "Flexing" our rafter with plywood blocks and clamps as discussed earlier, then bonding of the filler strip in, created a mechanical lock holding the arch. And by attaching each end of the rafters to the steel frame rails of the coach, I think its there to stay. The profile shape of  the rafter also allowed us to use the side legs to mechanicaly hold up the foam for bonding  and any plywood cross-members as required. Installation was not complex, becuase one side of the interior ceiling was rotted, it was removed right to the curved side caps. It was simple to just rest the new rafters , metal or wood onto the metal side rails and attach. The other side was still very strong, the interior ceiling was cut back flush with the metal rail. Where required pockets were mortised in, carefully with a chisel, to allow enough room to insert new rafters and attach with screws from the bottom through the rail. New foam was bonded, in between rafters, to the inside of the alum. roof and  new vinyl covered luan bonded and brad nailed to that. Looks as new. Our choice for steel rafters was one of availabily and convenience. Other materials should work as well.  Hope this helps,
Mike   

[54PrairieSchooner]

Sent: 7/26/2004 7:03 PM

Mike, thanks..an excellent post with a lot of details!

All of my rafters are starting to sag...not from leaks, but from old age and likely snow and rain weight from sitting in the abandoned car lot for almost two years and Lord knows how long with the PO..... and the fact that the replacement roof did not use the thermopanel construction method..the ceiling is some sort of pressed white cardboard..about 1/8 inch thick..it doesn't appear to have much structural strength.

Thanks much..I am scheming now!