Given: A special inspector notices on a mass timber building set of drawings a 8...

The IBC does not require structural composite lumber to retain the same nominal dimensions as the solid-sawn member it replaces. Instead, the minimum finished dimensions are determined from the heavy-timber dimensional equivalency provisions in Section 2304.11.

For a solid-sawn member having nominal dimensions of 8 inches by 8 inches, the corresponding minimum structural composite lumber net dimensions are 7 inches in width by 7-1/2 inches in depth. Therefore, option B is correct. The dimensional conversion recognizes that nominal solid-sawn dimensions differ from actual manufactured dimensions and that SCL products are produced to controlled net dimensions.

The 6-3/4-inch by 8-1/4-inch dimensions in option C correspond to the minimum glued-laminated timber equivalency for an 8-inch-by-8-inch nominal solid-sawn member, not the SCL equivalency. Option D incorrectly assumes that the SCL member must retain the original nominal dimensions, while option A does not match the required equivalency for either SCL or glued-laminated timber.

The substitution must also be approved by the registered design professional because dimensional compliance alone does not establish equivalent structural capacity, connection behavior, fire resistance, or load-path performance.

References/Topics: 2021 IBC Section 2304.11; heavy-timber minimum dimensions; minimum structural composite lumber net-size table.

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