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I'm planning an addition which will be 16' wide by 27 feet long overall. the roof will span the 16' dimension. my question is, if there is no plan to use the space above the ceiling for storage or occupancy, can I have a clear span of 16 feet with no supporting beam. Again, this is the roof. My guess is that I would use 2x8's for the rafter ties/ceiling joist, and also 2x8's for the rafters. There would be interior framing inside the addition, but there would be an area of about 15 x 16 that would be clear. The pitch of the roof would be about a 4 pitch.

Edit:

Thanks for the responses,

Yes the ridge will be centered on the 16' span. I don't want to use trusses if I don't have to since I will be doing basically all the work myself, and building them in place is easier for me. Also, I am matching the pitch of a small existing part of the house that will be removed and tying the new addition into the main building. In essence, I want to make the new addition fit the existing house / siding, not have to modify the existing building to fit a truss. I know I could get them close, but I'd rather do it myself. Also trusses would be more expensive.

My real question is can the room I'm building be clear of support beams. The ceiling joist would span the 16', and basically hold only sheetrock/insulation/wire for weight. the raters above would form the tops sides of the triangle and support the roof load. I do live in CT, where we can have a lot of snow (or not). I would assume that if there was a lot of load on the roof, the load would tend to push the ridge down and the walls out (and down), and put the ceiling joist in tension.

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    Typically you'd install engineered trusses that meet local and state load requirements. Are you building your own? – isherwood Jan 22 '16 at 21:59
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    Is this a gable roof or some other framing? Will the ridge be centered over the 16' dimension? – Comintern Jan 22 '16 at 23:22
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    Since the ridge will be in the middle of the span, the rafter span will only be 8 feet. Yes the ceiling joists will be in tension. The need to be toe nailed to the plate and hurricane clips added as well as nailing the rafters to the ceiling joists and those toe nailed too. – Jack Jan 28 '16 at 4:23
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The local IRC book would be handy for you. I have a few screen shots that may help, but only as a guide line. A building inspector will have the final say, but this is what they go by.

This does depend on where you live, for it has to do with snow loads. Roof cover factors in a bit too.

Span does not matter if it is 4/12 pitch or a 12/12 pitch. The span is not measured on the slope.

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2x8's should do the trick if possible tho double two up in the middle with a piece of plywood sandwiched inbetween for an expansion joint

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    -1, this doesn't account for type of wood or spacing of the joists. – BMitch Jan 25 '16 at 1:06

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