Metal Roof mounting dilemma


New Member
Nov 28, 2021
First time here. I am mounting 45 72-cell panels on the roof of my 50 x 60' hangar and I'm having difficulty determining the configuration based on the roof construction. It is an all metal building with steel purlins on 2 foot centers. The metal roof is mounted directly on the horizontal steel purlins, with 3" insulation between. There is no wood or other structure besides the purlins. The purlins are 2x4, on edge.

Here's the problem: Because of the 2' on center purlins I only have two options to mount the panels, which are 79x39". I'm using the Tamarak rail system, with S-5 Solar Feet. If I mount the panels in 'portrait' orientation, they can be close to each other on the horizontal plane, with 3 rows of 15 panels, but there will be an approximately 1.5 foot gap between each row of panels. I'm in New Hampshire and I'm concerned with snow sliding off and building up between the rows of panels. I'm also not sure how it will look aesthetically with the gap between the rows. On the other hand, the gap between the panels will allow them to run cooler.

The other option is to run the rails vertically with the panels in landscape, 5 rows of 9 panels. This would allow a continuous array, but I'm limited to a multiple of 9" distance between rails because the solar feet must be on a purlin, and the roof geometry only allows that every 9". The problem arises when I figure where the rails need to be to clamp the panels. There is a limited region on the panels where they can be clamped to meet the 50 psf snow load for our area. There is no configuration of rails that will meet that requirement without some of the clamps being in a section of the panel designated as only supporting 35 psf. The panel manufacturer states that if ANY part of the clamp is in the 35 psf region, the entire panel must be rated as such. I therefore assume I can't use this configuration without risking panel damage and voiding the warranty. I considered S-5 RibBrackets, but with no structure between purlins, I'm concerned the roof isn't strong enough to support such a concentrated load if they're not directly over a purlin.

Any thoughts on the gap between rows in the first scenario or any other mounting suggestions?



Photon Sorcerer
Oct 15, 2020
I don't think it would look bad to have the gaps on the first scenario... If you're worried about snow buildup, could you just install the heat cords all around (you kind of zig-zag them like a sine-wave along a stretch) for use during snow? I don't think they use much power really, a lot of people use those where I'm at to keep their gutters from clogging up with snow and ice...

EDIT: I guess an example shows they may use about 5w per foot on power:

You'd have to decide if that was within your power budget...