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Default Shed project: Roof trusses

I welcome any criticism on my roof plans. I'm not a structural engineer,
I'm only making educated guesses, and I promise you won't hurt my feelings
with good suggestions! The lumber isn't bought yet, my plans aren't cast in
stone, and I'd rather get it right the first time than have to clean up the
mess after it caves in under a snow load.

I'm putting a plain gable roof on my shed. I plan to call around to ask
about prefab trusses, but I have my doubts about how cost-effective that
might be. If they're not stock and already waiting in the yard, I don't
think a custom run of 12 units will be economical. I may end up building my
own.

I've built smaller (10') trusses using glued and nailed wood gussets. On
that job I used 7/16" OSB with good results, but with the shed's 12' wall
span I wonder if I ought to use plywood...? The cost difference is trivial.

The roof has a 12' span with 12" tails, pitched at 4:12, trusses spaced 24"
OC. My truss plan is a simple open triangle with a one-piece collar
tie/ceiling joist. I'd like to retain a little attic storage, but I could
add a couple of vertical braces at 4' intervals without impinging on that.

Local code calls for a 30PSF snow load. Roofing is architectural asphalt
shingle, so 10PSF dead load should be plenty. When picking rafter material
and looking at span tables, it seemed like there were certain grades of 2x4
that would carry that. But I don't think my local places carry such good
lumber so I'll probably go with 2x6 instead (I'll check available types and
grades before deciding; most of the local supply is Douglas fir larch, but
not sure of grade on the 2x6 stuff).

Lastly, I'm thinking 19/32" OSB for the roof sheathing. I know a lot of
people will only use CDX, but I can't quite fathom why yet.

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