Fred Bear writes: I was told by my inspector that the code doesn't allow "greenboard on a ceiling". Is this true?

Answer: Section 2509.3 of the 2006 IBC states 1/2 thick water-resistant gyp backing board can be used if the framing is 12" o.c. or less. 5/8" w-r-g backing board can be used on framing 16" o.c. or less. I must note this section only refers to "showers and water closets" and is referring to "backerboard" which I interpet as being used for tile or other like finishes. Back in the days of The BOCA model code, we did not allow w-r-g on ceilings by referring back to the individual gypsum manufacturer's written installation instructions. If you are planning on using it for a finish surface, I would refer to the manufacturer for their input.

SIde note: A change in 2006 IBC does not allow w-r-g backer board to be used as a base for wall tile in tub and shower areas and wall and ceiling panels in shower areas.