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Old 09-11-2007, 11:32 AM   #1
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rafter questions - structural


Hi all

I'm building an addition - approx 16x32 - onto existing camp. Walls are 2x6 standard height. Would like to frame it as a vaulted ceiling. I'm thinking of using 2x8 rafters 16" o/c to span the 16' width, nailed against a simple ridge board (also 2x8) along the 32' run at approx a 1:2 pitch, with rafters tied together at the top plate using 2x6 joists

I'd like to run the joists only at 48" centers as opposed to tying in every rafter pair, and then cut some simple 2x6 struts and wood gusset plates to turn each joist / rafter connection into a kind of exposed "rafter-truss". I've seen this done (similar) and I really like the look.

Questions:

1) Is a joist every 4 feet enough to tie outside walls together at top plate, to support the rafter structure in-between the joists, etc?

2) for the new gable end wall (16' width), do I need to somehow brace this wall back into the rafter structure to keep it from bowing in or out? (the other gable end ties into existing building / roof structure). If so, would some simple short connections - say from the last exposed joist to the gable wall - add enough structural integrity to the "ceiling" at this end to prevent and deflection in the wall? Would like to tie it together without ruing the look of the exposed rafter/truss at that end.

thanks
-randy

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Old 09-11-2007, 11:45 AM   #2
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rafter questions - structural


Randy; cant answer most questions but I think if you are going 2 x 8 rafters you will need a 2 x 10 ridge beam. plumb cuts on 2 x 8 will be longer than 2 x 8. I personally dont like tie-ins at 48" I think too far apart. Am shure a bunch of framers will be here soon to give exact answers.
FramerMan where is you?
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Old 09-11-2007, 11:51 AM   #3
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rafter questions - structural


yeah - thanks Jack - didn't stop to consider the plumb cut depth - appreciate the reply. look forward to hearing from some of the framing folks...

-randy
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Old 09-11-2007, 12:01 PM   #4
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rafter questions - structural


rtoni; uh oh I had another thought run run LOL LOL since you want to have visible trusses and cathedral ceiling I would think you would be way way easier and faster in the end to just have full trusses made for the whole roof. They can engineer them the way you want and in long term probably cheaper than your labor, material etc.
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Old 09-11-2007, 12:33 PM   #5
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rafter questions - structural


Thanks Jack - I did consider that (ordering trusses) - still leaves the question - is one every 4 feet good enough?

been going over a lot of different options - i actually enjoy doing the work so nailing up rafters along the entire run doesn't scare me (too much ;-)

I can do the basic rafters and get the sheeting on (which gets me to a stable structure and closed in) without hurting my brain - I could add some "truss" elements later as time permits - they'd be mostly aesthetic with any added structural integrity as a bonus

I can't space them out (tie in walls) at 4 feet (or more?) then the idea of the exposed truss loses it's appeal

-randy
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Old 09-11-2007, 09:01 PM   #6
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rafter questions - structural


rtoni: IMHO trusses 24" center, sheathing minimum 5/8 WITH CLIPS.
You have to run your ceiling 16" on center and without support they will want to roll.
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Old 09-11-2007, 09:47 PM   #7
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rafter questions - structural


Ok....read closely. You specify what you want, and the truss company engineer will design the trusses, for the spacing you like, and keep all the loads in check. I have built new spec homes with trusses on 8 foot centers, and 2X4 "purlins", on edge, between the top truss rafters, and ceiling joists, 2X4's on edge between the bottom chords. Now the trusses were engineered for the loads, both dead and live, top and bottom, and made a perfect roof.

If you go for 4 foot on center, you will need to think about the decking, and perhaps go with a purlin style roof framing for the actual deck sheeting.
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Old 09-11-2007, 10:33 PM   #8
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SEE!!!!!!!! Told ya a REAL framer wood show up LOL LOL Howdy JO
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Old 09-12-2007, 08:00 AM   #9
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Where did you see a framer????? Now my grandfather was a framer....I wish i still had it....the long, wooden box with the 3 different handsaws, the nail pouch belt....brass plumb bob, folding ruler (how long since some of you have seen one of those), steel square that was actually used for the purpose of square and true...and he knew the tables on the side...could cut a hipped roof from the ground. A mahogany and brass bound level....and I don't remember what else....he was a carpenter. If he were alive today, I cannot imagine what he would think....just about the tools we use today.
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Old 09-12-2007, 11:40 AM   #10
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thanks all - not sure if i confused the issue with the way i worded the original question

i want to frame the entire roof with rafters 16" on center - using the appropriate span tables, taking into account local snow loads, etc. - insulate and cover inside with t&g pine or something - walls tied together with either collar ties part way up the rafters, or joists at top plate - no thoughts about trusses involved yet

this is where i started to think about an exposed truss or a box beam built over the joists or something like that just for aesthetics - if i tie the outside walls together every 4 feet as opposed to every 16" - and this is strong enough - later on (time and energy permitting) I may want to create the a box beam around the joists, or maybe build it up to look like a truss - in either case the bottom chord still ties the wall together, and the rest is just there for appearance only - the real roof structure is still in the rafters 16" o/c

but if I have to tie the outside walls together every 16" I'd rather use collar ties farther up the rafter as opposed to joists.

so what I was really worried about is if the wall tie-ins at 4' o/c would be sufficient.

does this make sense?

thanks agian

-randy
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Old 09-12-2007, 07:42 PM   #11
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rafter questions - structural


The look you are trying to achieve will work, as I described, and will meet load requirements...again, call a truss company and let their engineer give you some guidance. If that doesn't fit, try talking to a contractor or your local building inspector and get some input.
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Old 09-13-2007, 06:40 AM   #12
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Quote:
Originally Posted by joasis View Post
....I wish i still had it....the long, wooden box with the 3 different handsaws, the nail pouch belt....brass plumb bob, folding ruler (how long since some of you have seen one of those), steel square that was actually used for the purpose of square and true...and he knew the tables on the side...could cut a hipped roof from the ground. A mahogany and brass bound level....and I don't remember what else....he was a carpenter......

Same here....when my grandfather passed away I saw all those tools and alot more left at his house (retired carpenter).
Wish I had put my dibs on all those carpentry tools, but I was just a dumb 16 year old kid only concerned with the car he left me: 1970 Olds Wildcat...(that I wrecked about 1 1/2 years later)..

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