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I want to install 23 305w panels on my roof. It's a flat roof constructed with 2x8 beams spaced at 24". There is no snow load to consider and we get occasional wind and rain storms a few times per year.

Is this structure sufficient to support a solar array? I can space each panel a few feet apart. Each panel weighs 41lb with a psf of under 2.5.

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    Have you taken up this question with the HomeImprovement.SE? Because since you're asking for structural integrity I think your question would be better posted there.
    – Erik
    Sep 9, 2019 at 8:59

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You need to state the specs for the entire roof (and perhaps the vertical/wall supports of the roof). In particular, the spans involved. In general, unless your spans are very short, say 8’ or less, 2x8 roof joists at 24” oc (on center) is not sufficient because of the loads required for humans and materials when maintenance work is done. The standard for common residential-sized spans, say 10’ or 12’ spans, is 2x10 joists at 16” oc. You’ll note that this is an increase of 26% of depth in your joists and 33% in frequency of joists resulting in a substantially stronger roof. While the 2.5 psf is a modest amount of additional load (since it is well distributed), the worry is the point load of a human or two working in a specific spot on your roof. If you and a friend can jump up and down on your roof right now without seeing or feeling any deflection of the roof, you’ll be ok. Another consideration is the work area around your panels, in case just one needs replacing one day. Are the panels strong enough to stand one while you work on an adjacent one? If so, then butting up panels against each other is ok.

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