Our city uses 2005 or 2008 IRC building codes to go by. I am not sure where in the code is specifies what drywall/sheetrock to use on the bathroom ceilings. I thought greenboard or just moisture resistant drywall was the norm. I found out today the local yards do not stock moisture resistant drywall in 5/8" thickness – only 1/2". This puzzles me because there are many builders here, and they surely would have to use 5/8" rock because common building has trusses spaced 2′ on center, meaning 1/2" would sag, especially the greenboard 1/2" as it’s even more prone to sagging.
Am I just fine to use 5/8" type x (for fire rating) rock on the ceilings in each bathroom? Is it worth driving out of town to get some 5/8" moisture resistant rock?