2508.5 Horizontal gypsum board or gypsum panel product diaphragm ceilings .

Gypsum board or gypsum panel products shall be permitted to be used on wood joists to create a horizontal diaphragm ceiling in accordance with Table 2508.5.

Table 2508.5
Shear Capacity for Horizontal Wood-Frame Gypsum Board Diaphragm Ceiling Assemblies

 

Material	Thickness of Material (Minimum) (inches)	Spacing of Framing Members (inches)	Shear Value a, b (PLF of Ceiling)	Minimum Fastener Size
Gypsum board or gypsum panel product	1/2	16 o.c.	90	5d cooler or wallboard nail; 1 5/8-inch long; 0.086-inch shank; 15/64-inch head c
Gypsum board or gypsum panel product	1/2	24 o.c.	70	5d cooler or wallboard nail; 1 5/8-inch long; 0.086-inch shank; 15/64-inch head c

 

For SI: 1 inch = 25.4 mm, 1 pound per foot = 14.59 N/m.

a.   Values are not cumulative with other horizontal diaphragm values and are for short-term wind or seismic loading. Values shall be reduced 25 percent for normal loading.

b.   Values shall be reduced 50 percent in Seismic Design Categories D, E and F.

c.   1 1/4-inch, No. 6 Type S or W screws are permitted to be substituted for the listed nails.

2508.5.1 Diaphragm proportions.

The maximum allowable diaphragm proportions shall be 1 1/2:1 between shear resisting elements. Rotation or cantilever conditions shall not be permitted.

2508.5.2 Installation.

Gypsum board or gypsum panel products used in a horizontal diaphragm ceiling shall be installed perpendicular to ceiling framing members. End joints of adjacent courses of gypsum board shall not occur on the same joist.

2508.5.3 Blocking of perimeter edges.

Perimeter edges shall be blocked using a wood member not less than 2-inch by 6-inch (51 mm by 152 mm) nominal dimension. Blocking material shall be installed flat over the top plate of the wall to provide a nailing surface not less than 2 inches (51 mm) in width for the attachment of the gypsum board or gypsum panel product.

2508.5.4 Fasteners.

Fasteners used for the attachment of gypsum board or gypsum panel products to a horizontal diaphragm ceiling shall be as defined in Table 2508.5. Fasteners shall be spaced not more than 7 inches (178 mm) on center at all supports, including perimeter blocking, and not more than 3/8 inch (9.5 mm) from the edges and ends of the gypsum board or gypsum panel products.

2508.5.5 Lateral force restrictions.

Gypsum board or gypsum panel products shall not be used in diaphragm ceilings to resist lateral forces imposed by masonry or concrete construction.

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