16" or 24" oc for Ceilings?

The inspector has the blueprints I submitted for converting an attached mother-in-law apartment into a couple of additional bedrooms for the house. He is supposed to call me this afternoon to discuss them and if someone would be so kind, I'd appreciate it, if you'd alert me to code for ceiling rafters, where I can come off as knowledgable during our discussion.

Right now, there's no ceilings in that part of the house and the only code which applies is the IRC, there's no local or state modifications on the subject of ceilings.

My plan is to frame the walls at 16" oc because theoretically, there's going to be teenagers over there, once I sell the place. I'd kind of like to get away with 24" oc for the ceilings (unless someone has a strong caution, a horror story or if it isn't code) because there's a lot more ceiling rafters (joists?) than there would be walls, since some of the walls already exist.

If someone would be so kind... Is 24" oc acceptable for ceilings and since I'm asking, does anyone think 16" oc for closet walls or a single wall to divide a bedroom from a hallway, overkill?


Thanks in Advance


ETA: The rafter span would be about 11' and some of it would have additional support from sitting on the hall wall. And, especially if I can get away with 24" oc for all or part, I'm intending to use the metal rafter hanger-thingys that I believe might be manufactured by Simpson.

How about 24" oc for the part sitting on the hall wall and 16" oc for the unbroken 11' spans?

Any thoughts?
Thanks.

 

Joist spans are established in IRC tables R 802.4(1) and 802.4(2), the tables list spacings of both 16 and 24" OC.

 

Thanks - I know there's no local code and the state simply adopted "Chapter 8: Roof-Ceiling Construction" of the 2006 IRC. Since I don't have a codebook, I suspected either would be acceptable, but because I'm waiting for the guy to call, I figured, I'd ask.

Thanks.

 

Just a little tidbit, in case someone never thought of this: As the roof pitch increases, the load on the roof(within the span itself) decreases; conversly, more load, if the roof pitch is more shallow.

Therefore shallow roofs need all that W bracing between the rafters and joists on shallow roofs. And why steep pitch A-frames need perhaps only collar ties up near the top and nothing else, which allows open space to live in up there.