Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 25 - Gypsum Board and Plaster
Section 2508 - GYPSUM CONSTRUCTION
Subsection 2508.5 - Horizontal gypsum board diaphragm ceilings

Universal Citation: 780 CMR MA Code of Regs 2508.5

Current through Register 1531, September 27, 2024

Gypsum board 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 FRAMED GYPSUM BOARD DIAPHRAGM CEILING ASSEMBLIES

MATERIAL THICKNESS OF MATERIAL
(MINIMUM) (inches) 		SPACING OF FRAMING MEMBERS
(MAXIMUM) (inches) 		SHEAR VALUEa, b
(plf of ceiling) 		MIMIMUM FASTENER SIZE
Gypsum board 1/2 16 o.c. 90 5d cooler or wallboard nail; 15/8-inch long; 0.086-inch shank;15/64inch headc
Gypsum board 1/2 24 o.c. 70 5d cooler or wallboard nail; 15/8-inch long; 0.086-inch shank;15/64inch headc

For SI: 1 inch = 25.4 mm, 1 pound per linear foot = 14.59 N/m.
a. Values are not cumulative with other horizontal diaphragm values and are for short-term loading due to 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. 11/4-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 11/2:1 between shear resisting elements. Rotation or cantilever conditions shall not be permitted.

2508.5.2 Installation. Gypsum board 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. All perimeter edges shall be blocked using a wood member not less than 2-inch by 6-inch (51 mm by 159 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.

2508.5.4 Fasteners. Fasteners used for the attachment of gypsum board 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 (o.c.) 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.

2508.5.5 Lateral force restrictions. Gypsum board shall not be used in diaphragm ceilings to resist lateral forces imposed by masonry or concrete construction.

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