As a licensed GC in residential construction, I consulted building code span tables almost daily. The tables included 3, 4, sometimes 5 species of wood, 3 or 4 lumber grades, and values for floors, ceilings, flat roofs, shallow pitch roofs, and steep pitch roofs. I can find no such tables for aluminum structural members. If such a creature exists, please share a link.

I am trying to design a solar carport with a shallow pitch roof, that utilizes the panels themselves as the roof surface - why build a roof to poke holes in it and cover it with plastic sheets that are warranted for 25 years? The concept is ultra-simple, like an oversized Erector Set: four 6x6 posts in the corners, an I-beam/L-beam header at the high end and low end, and the rafters resting on the header beams and set 39" apart, the width of each panel. Open span on the driveway side (east) is max 21'8" (measured horizontally) which is also the span for each rafter. The header beams would have a max span of 17' 8". Lower end cantilevered 9" beyond the outside of the poles/15" beyond the header beam. Upper end cantilevered 16"" beyond the outside of the poles/22" beyond the header beam. Total rafter length is max 25'. A third vertical post could be set midway on the closed (west) end of the carport for added stability.

The panels are 39.4" x 66.3", 42 lb each and there will be 20 of them. I am estimating about 600 lb of edging, end caps, fasteners, wiring, etc. in addition to the weight of the panels, beams, and rafters. I envision using large dimension aluminum C-beams as rafters so that only one thru bolt is required to secure the panels on either side - an aluminum cap with bolt though it in a "T" config. I-beams could be an alternative (think boat trailer rails), even though they might require more drilling and more bolts.

Additional details such as mounting to floor surface, cross bracing, etc. will be addressed as the plan evolves, but for now.......

1) Is there a span table or something similar that I can use for material sizing?

2) If no such document exists, what size primary components (rafters and beams) do I need? What rafter profile would give the best strength vs cost and size?

Thanks for any insights, ideas, caveats, suggestions, etc. BTW, I have contacted three structural engineers, all of whom said they wanted to work on this project, none of whom ever made an attempt to visit the site.