Solar Panels and Snow Load

[SteelPE]

Does anyone know of any literature that addresses snow loads and solar panels? Every time I confront the manufacturer of the panels they said they don't increase the snow load on the roof. It drives me crazy that this is never really addressed. Attached is a sample photo of a system my client wants to put on his roof. I find it hard to believe this type of system will not attract more snow because it would act like a "cheese grater". Not to mention this thing looks like it would put some concentrated loads on the roof.

 

[Triangled]

Design Snow Loads for Solar Paneled Roofs
ASCE webinar by O'Rourke

 

[SteelPE]

That seminar is 4 months from now, I don't think my client will wait that long.

 

[structSU10]

it is an on-demand webinar per this link:

http://mylearning.asce.org/diweb/catalog/item/id/333197/q/c=79&t=2132

 

[KootK]

I've got this which is not exactly recent.

And there's this from a supplier: Link

These are good but deal with wind and seismic only:

Seismic

Wind





I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Once20036]

If you get a 6" snowfall, that's all the weight that there is whether you have solar panels or not. I`d agree with the manufacturer
Will it change the load distribution? Instead of an evenly distributed load, now it's being concentrated on the rails down each side.
Will it create drifts? I think this is where it gets a little tricky. I`d lean towards "yes" in any location where the array is greater than 15' wide.

 

[Canuck65]

There are quite a few reports out there from reputable firms such as RWDI that do confirm that in certain configurations and layouts that the design snow load is not affected. These are specific to racking manufacturers. I do not have any I can put my hands on or share at this point in time. Reputable solar racking manufacturers get reports completed for their systems that confirm design snow and wind pressure information that is useful to structural engineers. Whenever I have worked on a roof top solar project in the past, we require the solar manufacturers (typically the racking suppliers) snow/wind report for their system before we will start work on the project. If they cannot produce a report, we do not do the work. They grumble at getting the reports completed as they are quite expensive, however, it is just another cost of business that they need to account for if they are going to complete their projects properly.

Racking layout must be considered, as does ballast layout for ballasted systems. You are correct that the point loads and their effect on the loading the roof structure must be considered.

There are many, many engineers getting the snow/wind reports, accounting for point loads, etc.... so don't let the solar people tell you differently. I do find that there are solar companies that just keep calling around until they get the engineer that is willing to sign off cheaply, without reviewing any background info, nor requesting reports, likely due to unfamiliarity with the in's and out's of this type of work. I would not recommend being that engineer.