N.Y.C. Admin. Code § BC 2509: Section BC 2509: Showers and Water Closets

2509.1 Wet areas.

Showers and public toilet walls shall conform to Section 1210.2.

2509.2 Base for tile.

Materials used as a base for wall tile in tub and shower areas and wall and ceiling panels in shower areas shall be of materials listed in Table 2509.2 and installed in accordance with the manufacturer's recommendations. Water-resistant gypsum backing board shall be used as a base for tile in water closet compartment walls when installed in accordance with GA-216 or ASTM C 840 and the manufacturer's recommendations. Regular gypsum wallboard is permitted under tile or wall panels in other wall and ceiling areas when installed in accordance with GA-216 or ASTM C 840.

Table 2509.2 Backerboard Materials

Material

Standard 

Glass mat water-resistant gypsum backing panel

ASTM C 1178

Discrete nonasbestos fiber cement interior substrate sheets

ASTM C 1288

Nonasbestos fiber cement flat sheets

ISO 8336, Category C

Nonasbestos fiber-mat reinforced cementitious backer unit

ASTM C 1325

2509.3 Limitations.

Water-resistant gypsum backing board shall not be used in the following locations:

1. Over a vapor retarder in shower or bathtub compartments.

2. Where there will be direct exposure to water or in areas subject to continuous high humidity.