Ceiling joist support

[tree grower]

Will soon build a 20 x 32 building for my Christmas tree sales. There will be no interior partition or post supports, so I need advice re: supporting the center of the ceiling joists (collar ties). The easy answer is to buy 20 ft dimension lumber, but it would need to be sawed special. I would like to avoid using trusses if at all possible--I'm a rafter guy. Two possibilities come to mind. 1, butt 2 ten footers together and splice them with a 4-footer. They will need to support me and a helper while we build the roof, but I won't be storing anything overhead. 2. laminate a carrying beam 32 ft long using 2x8s or 2x10s. My greatest fear with this option is that such a beam is heavy all by itself, and may sag in the middle. BTW, it will have 10 ft walls. I eagerly await some thoughts on this issue.

 

[Wolfy]

Don't hate me, but everything you said will sag. You would either need a steel or lvl center beam, or use I-joists.

 

[tommu56]

A real lumber yard will have 20ft 2x10's not a box store.

you could put in a temporary post and beam for construction and remove it when done

All that said I used trusjoists on a addition at my cabin and fell in love with them square lightweight and flat I would be hard pressed to go back to regular joists and they were cheaper to boot.

or build your trusses your self google truss plans

tom

 

[dfkrug]

My workshop is 25x25, and I bought a 30' steel I-beam, and used
simple select structural DF 2x8 wooden rafters. I went with a bit
bigger beam than the calcs called for so I can support 1000# on a
trolley hoist at mid span. No sagging, cost less than wood, and
weighs a lot less than wood.

 

[massey990]

ceiling joists and collar ties are two different structural members and are subject to differnt types of loads and resistances.

collar ties are generally placed 1/3 of the total height* below the ridge and help prevent the walls/beams from being forced outward.

ceiling joists are basically non structural and are for the most part deadwood to support the ceiling although their tensil strength does add to the overall strength of the structure.

* heigth from top of wall/beam to top of ridge.

 

[ray66v]

Don't hate me, but everything you said will sag. You would either need a steel or lvl center beam, or use I-joists.

+1 :thumbsup:

 

[Tdcw4]

Use trusses

 

[crazyal]

If you're looking to avoid trusses and don't plan on putting anything up there then just use 14' 2x6 nailed and glued together to span the 20' way. You'll need a good ridge beam to support the 32' span. My old neighbor did it by making his own truss for a ridge beam.

Basically he put up the walls with the end walls matching the roof pitch. He then used 2x6 nailed and glued together to tie the walls together spanning the 20' direction. He used 2x4s to support the 2x6s temporarily while he built the ridge beam (a copy of a floor truss) resting on top of the 2x6s.

I think he started off running a single 2x4 the entire 32' foot length nailed to the 2x6s and butting the ends of the 2x4s together. He then ran a second run of 2x4s with glue and nails to offset the joints. I think he used 12' long boards so the gaps were 6' apart. He then made what looked like a short wall and glued and nailed that on top of the two rows of 2x4s. He finished it off with two more rows of nailed and glued 2x4s. After that was done he cut diagonal 2x4s and wedged them between the horizontal and vertical 2x4s. The last thing he did was nail 2x6 to the sides of the vertical 2x4s going all the way from the bottom of the 20' 2x6s to the top of the roof. I think he even put a little bit of an arc to it so when he removed the temp posts it would settle level.

It's lasted 15 Vermont winters with no problems but I think it's a lot of work and I'm not sure how much he saved.

Think of these but with about a 4' height.

 

[Gordon Gould]

Another option you have is to use a scissors rafter system. You can build it like you do with standard rafters and joists except instead of a ceiling joist the scissor rafter runs from the plate on one side up to a point high on the opposite rafter. So it is a little longer than a joist. Connect the scissors where they cross. It is very strong. You would have to call it a simple truss.

 

[KennyG]

ceiling joists and collar ties are two different structural members and are subject to differnt types of loads and resistances.

collar ties are generally placed 1/3 of the total height* below the ridge and help prevent the walls/beams from being forced outward.

ceiling joists are basically non structural and are for the most part deadwood to support the ceiling although their tensil strength does add to the overall strength of the structure.

* heigth from top of wall/beam to top of ridge.

This is the right answer. If I understand the building you are planning, you don't need ceiling joists - they would be a waste of money. I would stick build it also, if you have the time. I've done a number of buildings about that size and found stick building to be cheap and easy. If you want the strongest possible roof (and like doing carpenter work) stick build a full hip roof.