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# Various mean roof height3

## Various mean roof height

(OP)
I was hoping to receive suggestions on figuring out various mean roof heights in building (significant for wind load evaluation). Structure has mainly a flat roof, with attic walls on its perimeter. But in elevetors location there are two "pop-ups", that tower over basic roof level (11 ft height). Should I treat their top level as mean roof height for whole building or only for its part?

### RE: Various mean roof height

I would check both roof heights separately and decide how much of a change it was actually making. It's possible the increased height won't make more than a a couple of psf difference in your calculation. If that's the case, I would just size everything for the higher load. If not, then design the building for one pressure but design the lateral support for your elevator room for the higher pressure and carry it down through.

PE, SE
Eastern United States

"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
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### RE: Various mean roof height

For the mean roof height, most times I would neglect small elevator penthouses. If you want, calculate the mean roof height as
Σ(Aihi) / ΣAi

### RE: Various mean roof height

IT IS AN ESTIMATE, BASED ON AN ASSUMPTION, BASED ON A GUESS. Please do not think that the wind load predictions of ASCE 7, or any other code or standard, are accurate to that level. Long return periods, estimated wind, estimated terrain, rough order gust and directionality, etc. You should use your best engineering judgement, but do not go to finer than whole integer values of precision - decimal values in wind loading are not useful. That said, use the arithmetic mean, that is, approximately average the roof height when appropriate. The C&C loads on pop-ups will be higher, but the MWFRS would be resisting wind based on averages.

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