Wallboard

[hookerp]

I need to hange the wall board in my bathroom. I read in one post that you can not hang the green wall board in the ceiling if the joists are not spaced at a certain distance. Why is that? The ceiling inside the shower area is at an angle, so I wanted to hang the green board. If I can't, what do I need to do in order the keep the board from getting soaked. Any special sealing or painting that must be done in the area?

Also, is there any code on the thickness of the wallboard? Or is it up to the building as to the preference? I have set everything for the 3/8 board, but I only find the green in 1/2 inch.

Thanks

[LazyPup]

Per the plumbing code specifications water resistant sheetrock (Greenboard) may not be used on a ceiling if the framing exceeds 12" center to center. (International Residential Code 702.4.2 & Uniform Plumbing Code 251.2)

Ceramic tile may be applied directly to water resistant sheetrock (greenboard) on the bathroom walls but may not be used to support ceramic tile in the shower enclosure. IRC 702.4.3 & UPC 251.2)

Water resistant sheetrock IS NOT to be applied over a vapor barrier (IRC 702.4.3 & UPC 251.2)

Backerboard (Cement boaard) must be used to support ceramic tile in a shower enclosure (IRC 702.4.1 - UPC-check local codes)

Backerboard requires water resistant building paper backing (IRC-per MFG instructions & UPC 807.1.3)

Water resistant materials must extend upwards 72" from the elevation of the finished drain (IRC 307.2 & UPC 807.1.3)

To the best of my knowledge greenboard is only made in 1/2"

Conventional sheetrock may be used on the ceiling. All seams should be taped and mudded with joint compound then painted with water resistant paint.