When Type X gypsum board is used as noncombustible protection over mass timber on the...

Option A reproduces one of the two permitted exterior gypsum-board fastening methods in 2021 IBC Section 722.7.2.2. Type X gypsum board used as noncombustible protection on the exterior side of mass timber walls may be attached using galvanized nails of minimum 12 gage with a 7/16-inch head and sufficient length to penetrate the mass timber at least 1 inch .

The code also permits ASTM C1002 Type S, W, or G screws, but those screws must likewise penetrate the mass timber a minimum of 1 inch . Options C and D are therefore incorrect because they specify only 3/4-inch and 7/8-inch penetration, respectively. Option B is incorrect because it substitutes 16-gage nails for the minimum 12-gage requirement.

Section 722.7.2.2 additionally requires exterior Type X gypsum-board layers to be fastened 12 inches on center each way and 6 inches on center at joints or ends. Panel-edge fasteners must be located at least 1 inch and not more than 2 inches from the edge.

These fastening details are part of the conditions necessary to claim the protection contribution in Table 722.7.1(2).

References/Topics: 2021 IBC Sections 722.7.1 and 722.7.2.2; exterior Type X gypsum-board protection.

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