by Jerry Peck - Codeman on Wed Sep 18, 2013 8:18 pm
David,
I will expand on my "Yes, one could have regular drywall, not even painted, down to the tub." comment with this:
- R702.3.8 Water-resistant gypsum backing board.
- - Gypsum board used as the base or backer for adhesive application of ceramic tile or other required nonabsorbent finish material shall conform to ASTM C 1396, C 1178 or C1278. Use of water-resistant gypsum backing board shall be permitted on ceilings where framing spacing does not exceed 12 inches (305 mm) on center for 1/2-inch-thick (12.7 mm) or 16 inches (406 mm) for 5/8-inch-thick (16 mm) gypsum board. Water-resistant gypsum board shall not be installed over a Class I or II vapor retarder in a shower or tub compartment. Cut or exposed edges, including those at wall intersections, shall be sealed as recommended by the manufacturer.
- - - R702.3.8.1 Limitations.
- - - - Water resistant gypsum backing board shall not be used where there will be direct exposure to water, or in areas subject to continuous high humidity.
You could install that regular drywall down to the tub ... unless ... unless you were to install "ceramic tile or other required nonabsorbent finish material" on the drywall, in which case the drywall would need to be water-resistant drywall ('MR', 'green board', etc).
While it may sound strange that the drywall does not need to be water-resistant until there tile or similar is installed on the drywall as the tile or similar helps protect the drywall from water/moisture damage; however, if there is no water/moisture then there is no need for the tile or similar material to be installed over the drywall, thus the drywall needs no protection.
Here is the potential problem when using regular drywall around a tub: The house is constructed (or bathroom remodeled) with regular drywall down to the tub, the work is complete, the occupant goes to a Big Box store and buys some tile and adhesive - oops ... wait a minute now ... they are not allowed to install that tile they just purchased over that regular drywall - who is going to educate those DIYselfers of all the things they are not allowed to do by the code?
Next problem is this: The house is sold and those 'really nice folks' installed that tile all the way to the ceiling to make the bathroom look really nice ... and no one has any idea that behind the tile is regular drywall, not water-resistant drywall.
Remember, though, the code is "minimum" and does not attempt to regulate common sense, stupidity, unlicensed contractors, or even licensed contractors, who do not know or do not care.
R702.3.8.1 is the code section which does not all even water-resistant drywall to be used as a tile backer board when there is a shower at the tub or in a shower stall, cementitious board is what should be used in those locations.
Jerry Peck - CodeMan
AskCodeMan.com
Construction Litigation Consultant - Retired
Construction and Code Consultant - Semi Retired