We are building a new house and our contractor typically does the ceiling joists 24" on center. My husband is afraid over time the sheetrock will sag (because we have a spot in our current house that did) and he wants to do 16" on center. This, of course, is extra money because of more trusses. The reason ours failed in the current house has to do with a leaky roof he let go for years, but he doesn't see it that way. Anyways, I would like to know from any of you builders or anyone else that would have some data or input on this.