I've always viewed the "origin" as being intended for a lightweight roof overlay. That would lend to the "solo" 5% increase that would net, in some load combinations, 15%. I would NOT read it that way without signoff from the building official and disclosure on the drawings/letter that that's what is being done. (a la Florida 'violating' the code or standards).
Were it my project, logically, the 5% overstress would apply to a load case or a load combination under the appropriate code, and I suspect there've been a few code change proposals (that I also presume failed) that would have clarified that.
Further, the 'overlay' in my mind, would typically be shingles, not all that typical with the "current" vogue for flat roofs. This would technically be a dead load, but unless there's some kind of offsetting effect, a change of occupancy (i.e. live load increase), adding weight (like solar), and changing insulation (higher snow load), these all "eat" from the same trough of allowable 5% increase.
I'd also add something about roof slope. We've seen enough roof collapses in the media, better to try to avoid them on the design/repair side, if possible.
Mike Mike - code change proposals are "free". No need to go the drastic step of joining the organization... I've gotten one approved. That or just call that Reid Middleton guy who writes a hundred code change proposals a week, he can squeeze yours in, I'm sure.
EZ building - I've referenced that provision in several damage reports calling for engineering to satisfy those requirements. One was a residential, the other was a poured gypsum roof from 1970. It shows up in Hurricane damage projects with structural and roof damage, there's a dollar limit in the FBC/FEBC for residential and a precedence lists, and I often see public adjuster estimates that include renailing of the diaphragm (for uplift), as a precautionary measure. T.L. Smith discussed that some years ago. And What's SID, anyway?
