Adhesive for steel solar brackets to aluminum roofs

I just posted a thread on what I did to mount mine. On an aluminum roof I would probably convince myself to put a screw in each mount in addition to gluing them. Polyurethane will bond pretty well to the aluminum, but it is a thin sheet and might lift from the plywood underneath. I didn't have to worry about that with the fiberglass roof.

YC 1 wrote:
You don't have to find a frame member. The wind load is low and the screws just add additional security. To prevent drilling into wires you can pre-drill very small pilot holes using several wraps of electrical tape on the shaft of the drill bit to make a depth stop. Then gently insert a small wire down the hole to test clearance. Be sure to use short screws when you fasten.

x2 Also use a short screw with wide threads for extra holding power.

You don't have to find a frame member. The wind load is low and the screws just add additional security. To prevent drilling into wires you can pre-drill very small pilot holes using several wraps of electrical tape on the shaft of the drill bit to make a depth stop. Then gently insert a small wire down the hole to test clearance. Be sure to use short screws when you fasten.

Thanks for that!

Installed 4 of the same Renogy 100 W panels that you have on our AF 811 last year, although not the same roof type, ours being TPO membrane there are similar considerations to take into account those being the covering not bonded to the substrate and uplift from traveling speeds and the occasional big blows. I would not be concerned with roof penetrations with the use of liberally applied RV sealant. Screws and lots of them are going to be your friend in the fact that your panels are not going to leave your roof! Granted the thin ply that is under does not provide great fastening it does give a certain degree of mechanical bonding which is what I wanted to achieve.
I did not feel comfortable with standard Z tabs giving enough holding strength, made our own with aluminum angle, 2 inch and 1 1/2 respectively the main feet being 4 inches long with 3 screws # 10 1 inch in each with 6 feel for each panel. Search Jack Meyer and Handy Bob for great solar install info. I "Love" my solar!

All very helpful! Indeed with the aluminum roof it's just stretched over the frame, and is loose. The sail thought opened my eyes on this that I may very well want to screw these in, as I will be traveling at up to 80mph, but I have no idea to know where the frame cross members are... I need to see if I can track down a blueprint somehow. And a wiring diagram to make sure I'm not drilling into a loom of wiring... argh. It's never easy, is it?

Ditto on one screw. I have seen the tape come off many things. Just the friction of the surfaces being compressed will add a huge margin of shear strength.

I don't think I would fasten solar panels to a aluminum roof without fasten them down with screws. Aluminum roofs are not glues down and are only fastened on the sides. I feel if you don't fasten them down with screws you are asking for them to act like a sail and try pulling the aluminum off the roof.

The only roof systems that I would glue a panel to is a fiberglass roof.

This is IMO

I've used urethane adhesive (Sikaflex is one brand) with proper preparation of the bond surfaces for panels up to 200W and had no problems despite thousands of miles of washboarded roads.
Make sure the adhesive thickness is correct (thinner is rarely better) and the surface area of the bond is large enough and it will never come apart - if you ever need to get it off the roof, you will have to cut through the bond with a sharp knife.

Sentinelist wrote:
I've seen a couple recommendations from long ago, but is there a de-facto standard product for this solution? I've got two 100w Renogy panels I'm planning to install in the next week and would rather not drill into the roof to mound the Z-brackets. Is it still recommended to throw some Dicor sealant on top of the contact part of the brackets as well? Thanks.

Very High Bond (VHB) tape from AM Solar. Yes, cover the bracket bottom with Dicor. This ensures that no water gets to the tape and loosens it up. The VHB tape works great, but I still don't trust it 100%. For this reason I would also use a single screw to mount the bracket to the roof. Extra insurance against high winds.