For the computation of low-rise C&C loads for the purpose of designing sheathing and for nail withdrawal calculations, a tributary area A is chosen as less than 10 sq. feet. This is because the area tributary to each fastener does not exceed 2 square feet, and the area tributary to each line of fasteners on a sheathing panel does not exceed 8 square feet (1sq m.). For our purposes, this distinction is not important, as the coefficients derived from A are constant for A < 10 sq. ft.