Gyp. Bd. at showers

Does the requirement prohibiting gyp. bd. in shower areas apply at fire partions behind fiber glass tub shower encloseures? If it does, does anyone have suggestions that would provide the 1-hour rating as well as the required soundrating?

Also if a true mudset tile is used at a firepartition does anyone have reports to support a one-hour rating and the required sound rating? The wall assmbly I'm looking for is a doulble row of 2x4 wood studs with a 2 inch air space.
Original Post
CBC 2509.3 does not allow water-resistant gypsum backing board over a vapor retarder in shower or bathtub compartments, where there will be direct exposure to water, or in areas subject to continuous high humidity.

With regards to a pre-fab shower unit/compartment (for a roll-in shower), does this imply that the gypsum is permitted in the shower compartment if a vapor retarder is not proposed? Or can gypsum be installed "under" (rather than over) a vapor retarder?
It appears this is an apartment or hotel condition you are asking about.
In order to maintain a fire rating, the gypsum board must be continuous to comprise a wall assembly. The wallboard behind a fiberglass tub/shower unit (presumed as a single piece unit of tub with attached shower wall panels) is allowed. Caveat being that any penetrations necessary for piping, conduits, etc. are properly fire sealed.
Per 2509.3 item 2; the area beyond the shower walls is not considered "direct exposure" to water as the shower wall panels cover the wallboard and control the water. Nor is a residential bathroom condition where intermittent use is typical an area of continuous high humidity.
To maintain fire and sound ratings; there are good combined fire/sound rated wall assemblies in the Gypsum Association Fire Design Manual (downloadable from the Gypsum Association website) and there are manufacturer proprietary wall assemblies as well that need to be investigated by the Architect to prove the wall fire and sound rating is provided.
Hope this helps.
Water-resistant gypsum board or 'green board' per Section 2509.2, is not allowed to be used behind tile "in tub and shower areas', where there is high water exposure, BUT green board is allowed behind tiles in water closet compartments where it does provide effective resistance for a less severe moisture condition.

Note that Section 2509.3, location 1, does allow green board behind approved water-resistant finishes other than tile in the walls and ceilings of shower and bathtub compartments PROVIDED there is no vapor retarder installed on the inside face of the green board.

The 2006 IBC Code/Commentary indicates that the installation of water-resistant membranes on both sides of the green board traps water inside the wall and causes the gypsum board to decompose and fail.

Further, per Section 2509.3, location 2, the IBC Code/Commentary indicates that green board is not allowed in areas where there are extreme moisture conditions with direct water exposure to water or high humidity, such as saunas, steam rooms, gang showers or indoor pools.
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