Posted by Ray Strang on March 09, 2004 at 04:11:35:
In Reply to: Designing a great room posted by Stephen Roberts on March 08, 2004 at 15:21:15:
I'm not talking about your particular case, but, in general, a person would need at least a ridge pole (that is a 2x "one size bigger than the rafter") or a beam to catch the tops of the rafters, and to place the collars at least 1/3 of the height of the truss below the bottom of the ridge pole. The rafters must be sized with the collar condition in mind, since there is a moment in the rafter once you collar it( the higher the collaris placed, the bigger the moment). Once you have a moment, then you have a force pushing the top of the wall outward, and you must account for it, both at the top and bottom of the wall. Then there is the problem of rafter bearing at the outer walls: for whatever size rafters are required, the lower (interior) edge of that much of the rafter must be supported on bearing wall (or in some other way) in order for the required section of the rafter to be working for you.Then you have hurricane anchorage and venting issues to consider. IBC 2000 has nailing requirements for some parts of this assembly, I think.
I'm making it sound more complicated than it is, but you should probably consult a professional who is familiar with local codes and conditions.
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