another roof mounting question

[bike4mee]

I'm mounting a solar panel. I have a seamed room with screws. In mounting the angle brackets I removed selected screws and replaced them with self tapping larger screws. The screws never seem to bite real well and a few were loose. I don't trust these screws in a thin tubular aluminum frame member. It seems I'm only getting a few threads to bite. I think I'm going to drill all the way through and use carrage bolts pushed up from the inside then nuts and washers. Anybody try this before. I know 4WC mounts a lot of racks to those cross members and they hold. What screws do they use? Glue? I know I need to silicon. Thanks for any ideas

 

[ntsqd]

If you don't expect to need to remove it I would suggest using 3M 5200 Adhesive/Sealant in place of the silicon. Better bonding and sealing than silicone, so it will last longer.

Wood screws seem to have a higher helix angle (fewer threads per inch) than do sheet metal screws. Which were you using?

There is a device known as a "Riv-Nut" which when properly set will give you machine screw threads down the middle of what is basically a pull-rivet. These come in a range of metals, for an aluminum structure I would use aluminum riv-nuts to avoid the dissimilar metals galvanic corrosion problem.

 

[JHanson]

I mounted Yakima racks to our first FWC by drilling all the way through the roof through frame members, using bolts and fender washers, and sealing each hole well. It worked without trouble, and supported two sea kayaks, so doing the same for a solar panel should be simple. You don't want to chance that thing flipping off on the highway . . .

The alternative is to use the Global Solar semi-rigid panels, which attach directly to the roof with adhesive backing, and leave no more than an inch of wind profile/overhead clearance issues. We have two of those.

 

[Cerdahl]

Since I had the rack rails on the roof, I attached my solar panel to one of those and it's been on a solid 3 years with no problems. Regarding which screw to use for installing direct to the roof, I'd ask FWC. They've been very helpful with my questions as I've installed upgrades over the years.