Ceiling joist support

[Army grunt]

Build it with a gambrel roof This will give yo open vaulted look. Its easy an its been used for many years.
Army Grunt
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[Gordon Gould]

Oh boy, these threads are fun. I think I'll throw in my 2 cents, get a beer and sit back.

My recollection of the building code is that collar ties, rafter ties and ceiling joists are three distinctly different things. Collar ties, as noted are in the top 1/3 of the peak, prevent uplift splitting of the roof, and are not intended to prevent wall spreading. rafter ties are usually about 1/2 way up or less and are qualified to prevent spreading of the walls. Ceiling joists can function as rafter ties if required. Depending on the loading conditions, rafter ties can be allowed as much as 4 foot spacing.

If proper ties are used, the ridge pole sizing is immaterial, since it only stabilizes the rafter spacing. Using a large beam on the ridge will allow you to do away with ties completely if you can prevent wall spreading. I know a structural engineer who put a peaked ceiling on a 30 x 30 room by designing a steel belt to wrap the top of the walls.

Given the problem originally stated, I still think rafter ties and no ceiling joists are way to go. Maybe collar ties are now required by some codes, but they didn't used to be. I've built some good sized roofs with just rafter ties on every other rafter and they passed inspection.

Very good explanation Kenny.
If it were me, like Kenny also suggested, I think I would go with a 16' rafter tie down as low as I could get it. I would probably hang the center from the ridge with a 2X4 to prevent self sagging. Or you could do the same thing with a pair joists, one 10' and one 12' or 14'. Butt the 2X4 hanger to the end of the 10'er and let the 12'er run by.

 

[tree grower]

This is entertaining and informative reading what you guys post. My use of the terms ceiling joist and collar tie interchangeably was sloppy. I know collar ties are near the top of the rafters, but I was using the term to convey the message that the joists are intended to prevent the walls from spreading. I am not totally opposed to using trusses, but this project will be heavily skewed to a one-man operation (me), and trusses are not easily installed by one person. Besides, even if I can get some help, hoisting trusses up to a 10 ft wall ain't easy. Regarding the gambrel roof, it would need to be built while walking on the deck. If I can walk on the deck, I can place common rafters easily alone. Scissors truss and vaulted ceiling- not my cup of tea.
Tom's trusjoists and Crazyal's flat joists have appeal. I'll have to see what the lumber yard has available. This whole exercise is easily solved if they have 2x8x20s.

 

[crazyal]

I'm pretty sure you can, if not I know 20' 2x10 and 2x12 are pretty common, I bought several a few years ago when I built my house. You could always rip a 2x12 and get a pair of 2x6. Finding 16 or so nice straight ones may be a little harder. If you're looking to save a few bucks you could look into rough cut from a mill.

 

[tree grower]

Update- I stopped into my local (non-box) building supplier, and discovered that 20 ft dimension lumber is as common as dirt. Problem solved. In my forestry work my mind is set to think in 16-ft increments , and any logs greater than 16 ft are rare and special-ordered.

 

[turnkey4099]

Update- I stopped into my local (non-box) building supplier, and discovered that 20 ft dimension lumber is as common as dirt. Problem solved. In my forestry work my mind is set to think in 16-ft increments , and any logs greater than 16 ft are rare and special-ordered.

Just my input. Re: trusses. The truss company usually delivers them on-site _on top_ of the walls. I would use them if you aren't going to store anything up there. Quick, easy and probably not much more expensive than stick build.

Harry K