Approx. Roof load weight per square foot for PV system

[brantech]

Hi
I am new to the forum and also to PV installation
I have a metal structure ( Barn/Shop) in Socal with a East / West exposure ( building ridge runs North / South ).
Pitch is 4/12 with 26 gauge R panels and 8"x2.5" zee purlins spaced 60" apart (EW) and supported @ 21' running parallel to the ridge.
Does anyone have an idea of the approx. roof load weight per square foot for PV system ( including panels, racking, micro inverters, etc.?????)
I need this info to determine if I go forward to the AHJ for the solar project of use another structure
Anyone have any experience with this type of building and any help with what type of racking to use would be helpful

Thanks,

Johnoutbuilding.JPG

[inetdog]

Just a heads up that the weight load of the panels may be small compared to the upward force on the panels in some wind conditions. You have to design your mounting to handle both force directions.

[sdold]

I just finished installing my own 16-panel system with microinverters. The weight of the system was 3 lb/sqft. The "design wind uplift" was 26 lb/sqft and down force was 19 lb/sqft for a similar roof pitch as yours and 100 mph basic wind speed. That equated to about 273 pounds uplift per attach point (I used 28), which were spaced 4' apart on each rail. This satisfied the AHJ, but I'm not a structural engineer so don't rely on these numbers too much. I used ASCE 7-05, the sections pertaining to "Partially enclosed buildings". Doing these wind calculations was the hardest part of my 16-panel install, the rest was easy by comparison. So as inetdog said, the wind can cause big loads, up and down.

I used Prosolar Rooftrac which I'm very happy with, but I don't have anything to compare it to. Racking all seems pretty similar, mine is no-frills. You can buy WEEB-PMC washers, lugs and lay-in lugs to make grounding easier, Enphase has the Integrated Ground version of the inverters, so it ends up being a very simple install.

One thing that helped my project was involving the people at the building department early on and throughout the project whenever I had a question about a code interpretation. The result was that I wasn't afraid of the inspection, since we had discussed most of the system ahead of time.

Steve

[brantech]

Roof loading

Thanks for the info regarding both the wind considerations and racking
Just on a side note.... what was the spacing on the purlins for your building?

Thanks Again,

john

[sdold]

mine is a house with scissor trusses, on 2 foot centers. But I assume the wind calcs would still apply.

[inetdog]

mine is a house with scissor trusses, on 2 foot centers. But I assume the wind calcs would still apply.

Yes, just the loading on individual supports would be different.
One more thing that needs to be taken into consideration is that each support needs to distribute its load seamlessly into the member it is attached to without weakening it. In some cases that may require sistering a piece of 2x4 or 2x6 to the truss member and using a bolt rather than a wood screw into the truss or purlin.

[leroysolar]

im totally new to this site but I was wondering if someone does this calculations on this site or if there is an easy calculations. I want to install solar on my barn. 40x60 with standard trusses at 24" made with 2x4s what else data do i need?

[inetdog]

im totally new to this site but I was wondering if someone does this calculations on this site or if there is an easy calculations. I want to install solar on my barn. 40x60 with standard trusses at 24" made with 2x4s what else data do i need?

There is nothing on this site, but I believe that the major suppliers of racking systems offer calculators. Not sure whether you need a customer login or not though.