When Two Skins Meet: Roof Raise Skinning the Bus

[CCBlythe]

Hi All! Thanks in advance for the assistance.
In raising the roof and placing the new sheet metal....what are you all doing when two pieces of sheet metal meet in between two hat channels? How are you securing the two pieces? While the replacement rivets are securing at the original location (up the hat channels), what measures are taken at the points of intersection BETWEEN hat channels? And how much overlap are you allowing for one sheet metal over the next? Also, if the two pieces of metal meet exactly at a hat channel, are you using the line of rivets to go thru BOTH pieces of metal?

[Downtownterrybrown]

When I laid them out I kept with the original sheet length of right at 60" I think. That came to something like 1" of over lap on each side. I started at the back and ran the sheets forward having a seem at every other spar. Before I cut any of them though, I had braced all the way down each side with 3 sections of cross bracing and another center bar in the "x". Big ole mess to get around in inside the bus while working, but totally necessary for ease of raising. After that it was cut and it only took two of us to turn the jacks (opposite sides, caddy-corner) and it raised the whole damn thing. So easy I could have simply pushed up a little and ran the nuts out. Oh and I also did a little math and continued the rivets from the originals and did the seams like that.

P.S.dont go too overboard with the seam sealer or caulk or urethane or whatever you use. You'll be wiping a lot of it off.

[rossvtaylor]

From the factory, all sheet laps happen over a rib. We try to make our roof raises look as factory-made as possible, so we lap the new panels in the same places and use the factory rivet spacing. Our lap joints at ribs generally cover both sides of the rib channel, so that overlap is 4 inches or so. We seal the joint, and add strength, with 3M 5200 adhesive sealant.

If you need to lap the panels and make a joint which is not supported by a rib, you want to make sure that your panel structure has enough strength to hold a rivet securely. On thin sheet metal, especially with beefy rivets, the rivet may not act as it was designed...it can expand all the way to the head, which doesn't really hold the joint well. So, if your sheets are thin it's a good idea to add a washer on the inside of the rivet. The rivet then pulls the washer against the inside skin and pulls the joint together. That, combined with a good sealant, can make a strong lap joint.

EDIT to add: I just remembered that we showed the use of washers in one of our roof raise videos. And, in places like the new horizontal joint over the windshield, I add a strip of 1/8-inch thick steel across the seam and rivet through that. That adds strength to the lap joint and also stops "oil canning" while you drive. That strip is easy to place over the flat part of the seam, but for the curved front corners we use washers behind those rivets.