attaching solar panels

Wood screws work fine.

I used #10 stainless sheet metal screws in 3/4" particle board, to attach 1/4" thick aluminum brackets for panels. Dicor under, Dicor onto the screw before driving it in, Dicor on the screw head after. I had a better luck with Geocel RV Roof Sealant than with Dicor. Either one works, but Dicor cures slower, shrinks a lot and bubbles.

Length of the screw should be longer than 1" if you hit the rafter.

This is what I am going to do with my roof situation...

I am totally against drilling into the roof on my OFF-ROAD POPUP trailer which is made up of Fiberglass with foam under that between 2-3 inch wood rafters every so many feet apart...

I don't think I would be able to stand on my trailer roof...

I have a pretty good solid edges of the roof especially on the sides near the top.

I am thinking of mounting metal brackets on the side edge to support lite weight Aluminum UNISTRUT angles across the roof. This can lay on the roof but not drilled into the roof anywhere. Maybe in the middle area of the roof I can dicor-in some additional material to go between the unistrut and the fiberglass roof.

something like this maybe on both front and back ends of my roof where I have room for panels...


This shows mounting to the top edge of the roof but I was thinking of mounting to the side of the roof and extend up abit and then mounting the unistrut. I have good strong back board on the sides portion of the roof.

The beauty of the Unistrut Angles you can slide the mounting hardware to fit almost any installation you come up against...



No harm to the roof itself...

Roy Ken

Almot wrote:
I used #10 stainless sheet metal screws in 3/4" particle board, to attach 1/4" thick aluminum brackets for panels. Dicor under, Dicor onto the screw before driving it in, Dicor on the screw head after. I had a better luck with Geocel RV Roof Sealant than with Dicor. Either one works, but Dicor cures slower, shrinks a lot and bubbles.

Length of the screw should be longer than 1" if you hit the rafter.

The FW has 3/8" decking and 1/8" aluminum brackets so that a 1/2" leaves 1/2" more screw. not sure where the rafters are suppose to be 16" centers don't know if a stud finder would work to find them.

Roy, it will be cheaper to get a regular square aluminum bar 1.5 or 2" and another short bar underneath - near gutter. Something like SMK did. Result will be the same.

Holes - not a big deal. There are more people who installed panels drilling holes in the middle of the roof than any other method. You already have dozens holes there.

Walking - when I walk on 3/4" particle board, I'm trying to move on all four and not to step between the rafters. Every time when I do step in between, I can feel it flexing. I'm under 170 lbs.

Screws - the thread on wood screw is coarser than on sheet metal screw, a better grip in soft particle board but I still don't trust it. Especially with big 24V panels and/or if tilting is in plans. Each one of my mounting brackets has at least 2 screws in the rafter, and then some in just particle board. Screws need to be a) stainless, b) fully threaded and c) with pan or hex head. It was easier to find sheet metal screws to these specs than wood screws.

One tip - don't pre-drill the hole if you are not hitting the rafter. Or use the smallest bit you have. Normally the size of pilot hole in "soft wood" for screw #10 is 1/8, but particle board is softer than any soft wood.

The FW has 3/8" decking and 1/8" aluminum brackets so that a 1/2" leaves 1/2" more screw. not sure where the rafters are suppose to be 16" centers don't know if a stud finder would work to find them.

One of the newer stud finders should work. What I did was find the rafter locations from below, in the cabin. It was relatively easy once I found that a roof vent opening was against one rafter. That made it easy to transpose measurements on the topside.

Before I started, I was told - good luck finding the rafters. So I bought "one the newer stud finders" ;) that cost $60 on Amazon and getting stellar reviews. Drywall installers writing those reviews have no clue what difficulties we are facing here. The accuracy was mediocre, 1" at best, but the rafter was mere 1.75" wide.

Per my request the manufacturer emailed me diagram of ceiling assembly and it was not very useful, other than telling me 1.75" width and that 2 rafters were not a regular spacing. The centers were 18" BUT at the rear and at the interior partition it was 10" and 14".

Yes, you can find them from below but how are you going to transpose this accurately to the outside?

Yes, bathroom vent and A/C are always sitting on the rafters but transposing it from there to the edge of the roof with 0.5" accuracy is not easy.

50 cent rare earth magnet helped me a lot, you slide it across the roof in the approximate location of rafter and find screws holding the 3/4" particle board. They "should be" in the middle of rafter, but $10 workers are not too accurate, screw heads were all over. You want to find those screws anyway, to avoid drilling right into the screw.

In the end, after checking and re-checking my markings obtained using all the above methods, I had to drill a very thin pilot hole where I thought the rafter center was. Where rafter was not expected, I didn't drill any pilots. Once the pilot went right into the edge of the rafter, now I knew where the center was, closed the first hole with toothpick and glue (it was tiny, a "dowel" that thin doesn't exist), and drilled another hole in the bracket. On another occasion, when checking the rafter through the pilot with thin wire, I found lighting wires.

It was fun.

PS:
in the retrospect, there could be a reason why my super-buper ultrasound stud-finder could barely see the rafter under 3/4 particle board: rafter was too far below. There was often a gap 1/4"-3/4" between the particle board and rafter. Don't try squeezing this gap down to zero, stop when Dicor starts coming out from under the bracket. In my trailer the ply was not screwed to the rafter in the middle of the roof, except for where there were 2 adjacent sheets of ply.

Sometimes a good morning frost can help you locate the framing, especially on the sidewalls but they might also show up on the roof. Get out there as the sun comes up before the frost melts. Play with temps inside the 5er to improve contrast.

Yes, with condensation on EPDM roof - like frost melting or morning dew, the rafters can be seen sometimes. Where I was installing it, there was no frost but plenty of dew in the morning.