Looking at a set of plans for a new building. 12/12 slate roof over 5/8 ply on trusses @ 24″ oc. Does that sound right? 20 psf live load, 20 psf snow load. Can’t tell you the wind load cuz there’s an error on the drawings that I need to get clarified tomorrow: it says “Basic wind speed – 950 mph”. I hope that’s not right.
“Put your creed in your deed.” Emerson
“When asked if you can do something, tell’em “Why certainly I can”, then get busy and find a way to do it.” T. Roosevelt
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Some slate is heavier than others.
but the way those spec writen is hogwash. Snow load IS a live load!
if the slates run fifteen #/sq, the total dead load might fit in at just about twenty, but that live load at twenty is light. I know some southern locations do still only require 15-20#/ft live load.
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Only detail I have found for the slate says it is 1/4" thick. So are you thinking that the roof design is ok? Is there going to be enough deflection of the 5/8 ply with supports at 24" to cause a problem? I don't know enough to make a decent guess, but I would think the rigid slate would want a stiff roof, whereas the flexible shingles would not be bothered with some deflection.
Overall I think the structural portion of the plans basically suck. just drawn kind of odd, looks like several missing details."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Well, 1/4" slate might only be 10-12#/sq and your area might only require a 20# live load, so it sounds OK borderline.
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OK borderline
Is that like "can't see it from my house"? Appreciate you comments though."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
I guess what I mean by that is that I would want to double check efvery stage of the engineering design and specs, possibly going to a 19.2" oc layout or 3/4" decking
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Is there a slate roof design source that I can research? I hate to challenge the structural engr without a little backup."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Not that I know. Slate manufacturers will just state that the structure must be designed to handle a ______#dead load with such and such max deflection. The way to check that without direct challenge to the engineer is to look up the slate manufacturers specs, and the ASK politely does this roof structure as designed meet these specs?
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