I have a 100 year old townhouse with 3×8 joists (true rough cut, not nominal, and *very* dense), 24″ oc, running side-to-side 16′ into pockets in brick walls. Over that are pine boards of varying width — nice wood! — then tarpaper (I assume) and decades of tar/emulsion topcoats. There is a slight slope (4-5%?).
I’d like to pull up the old roof and replace it, and I was thinking about recovering all that nice old pine, at the same time, and resheathing with SIPs for their insulating value — but they’d have to be strong enough, laid flat, to support foot traffic (the view of the city from up there is spectacular). Are any of them that strong?
This is my first flat roof. I plan to expose the 3×8 beams wherever practical.
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Come on over to my house and bounce on my roof!, actually you won't bounce very much and mine has no support! I span 30 feet from side to side and once I'm done I'll divide up the space underneath to enclose rooms so I'll meet the panel manufactorers recommended no more than 10 foot span unsupported.. from the sounds of it you support every two feet so you should be OK..
Actaully Sips are very strong! I cantalivered one over a part of my house and only toe nailed it from one edge (leaving the other edge hanging in the air) all summer myself and another guy put all sorts of stuff on that roof.. Hundreds of pounds plus my fat butt and another fat butt.
The only thing holding it in place was the spray foam used to connect it and some small toe nails! Didn't sag an inch!