huangyhg

roof framing help
gents,
for ya'll that do alot of residential conventional framing:
i've agreed to help someone with her new house. its 7k square feet with a lot of open areas. i have a few question, which may seem elementary, but most people don't really grasp.
1. rafters: what do ya'll do if the rafter and ceiling joist aren't parallel? (no truss action) some of my rafters will be spanning 22' at 9/12 pitch. do ya'll turn the ceiling joist parallel with the rafters, even if is not the short direction of the ceiling joist span? do i put of bunch of knee walls in the attic to shorten the span of the rafter so i could use 2x8's?
2. ridge board: do ya'll support each end of the ridge board at the hip valley with a packing stud? if so, would ya'll put in a double or triple 2x ceiling joist under each packing stud location? it just happens that this location is in a 20' span of ceiling joist.
any guidance would be appreciate. i'm a rookie with roofs.
schoolie
you need to get some professional help on this one...
running ceiling rafters perpendicular to the roof rafters is inviting disaster!! 22' spans need help!! and ridge beam needs special attention.
why not use roof trusses and get the local truss fabricator to help out. then check the house for wind/seismic, anchorage, etc.
get some help...for your own peace of mind.
sometimes you can run low collar ties right on top of, and 90 degrees to, the ceiling joists that are going in the wrong direction. or run the ceiling joists the long span (you can put midspan support beams in, so long as you strap the joists together across it to maintain tension ability if you want to keep the size down). with cut up custom roofs, it's often impossible to always have the ceiling framing parallel to to the roof framing.
the building code has default language to regarding purlins, and braces to reduce rafter spans in conventional roofs (i'm in california, so i couldn't tell you where it is in the ibc). support locations still have to be provided, but the way it's written will give you a jump start on wrangling the mess of different spans. at times, i have placed max. rafter span and the purlin bracing code text directly on the plans and let the contractor just work it out to comply. it's difficult to clearly show purlin bracing without a lot of drafting. you do of course, have to make sure that bearing locations are available to brace too, called out, and are adequately sized.
yes, forces at ridges, valleys, and hips have to be accounted for somehow. if you don't have ceiling joists etc. to create truss action, then you have to run beams or brace points or something to support them. this occurs frequently in hips and valleys, where you often don't have one on the opposing side to push back on.
trusses are a great solution to all this, but i bet it's not an option or you wouldn't be here.
trusses for the win especially because you want a flat ceiling! it will be a lot cheaper and less headache with trusses. i agree, you will need a professional help. you will need a lot of cad detail and it wont be sufficient if you draw everything from scratch.
how bout just put blocking between the rim board and first ceiling joist (maybe to the second joist) and let gyp board ceiling act as a tension tie?

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