PV Panel Clamps On Standing Seam Roofs and Non-Structural Metal Roof

[A Renaissance Man]

This question is actually two questions but both are related.

I started seeing these Standing Seam clamps that allow you to install solar panels on Standing Seam Roofs. My concern is that ASCE7 applies an uplift force to the solar panels and I can't see the clear load path from the clamp, into the vertical seam and from there into the roof framing members (since standing Seam Roofs have minimum positive attachment).

Second part of the question is the same company that created the clamps also have a top flute connection to metal u-panel decks clip. But many of these metal u-panel are more "roofing material" and not a "structural" deck or as the roof diaphragm. In those cases usually there is plywood sheathing underneath the metal decking (and the rafters are parallel to the flutes). Since the NDS has a minimum embedment depth and screwing/nailing into plywood is based on the ESR of that roofing material, I don't feel comfortable allowing them attach to the metal deck roof. I am getting push back when asking them to lag into the roof rafters instead of attaching to the metal deck.

Has anyone else run into this issue or is this just me overthinking.

Thanks,
Overly concerned engineer

 

[GeorgeTheCivilEngineer]

UK guidance is that solar installers need to seek expert advice (i.e. the roof panel manufacturers) when clamping to the standing seam.

I see a lot of assessments which ignore that part of the load entirely and often don't even consider the purlin (although if attached via the roof cladding and not via a point connection to the purlin itself I am reasonable happy that the uplift forces won't exceed the original design loads).

However... there aren't any failures I am aware of. Need a bigger storm.

 

[Aesur]

I haven't touched solar connections in 4+ years, however when I was doing hundreds of megawatts of racking design a year we used S-5 clamps: Link. They have load testing for clamp types with different panel types that was commonly used. I forget how we dealt with the panel itself, but I believe the tests either accounted for real panel attachment or we added screws in the panel and required sealing around the connections. As for attaching to plywood, check out the APA E830D: Link.

 

[Once20036]

My last conversation with a solar company was interesting. This may have been 4 years ago.

ASCE requires wind suction loads applied to the roof and roof structure. I don't recall the specifics, so let's say that the minimum 16psf governed the design.
The solar company indicated that their 6psf system didn't need any structural attachment to the roof. When questioned, they claimed that they had run their own wind tunnel studies on their system and found that the ASCE loads weren't applicable to their common installations, and they didn't need to meet the 16 psf minimum requirement. They would not share any of this test data with me.

I wonder if you`re experiencing something similar.

 

[Aesur]

@Once20036 - I have seen many wind tunnel studies over the years for PV panels on roofs and ground, with and without parapets, shielding by other panels, etc. and even the SEAOC PV studies and can say that the results vary significantly from manufacturer to manufacturer and that it's almost impossible to account for all possible roof types, parapet heights, slopes, etc. This is why even when using those studies the 16 psf minimum was always used by those manufacturers at the time, things could have changed in the past few years though. If they don't have a wind tunnel study, SEAOC PV documents and ASCE 7-16 have some great guidance on loading for PV now.