722.4.1.3 Multi-wythe walls with airspace.
BC § 722.4.1.3
Where a continuous airspace separates multiple wythes of the wall or partition, the total fire-resistance rating shall be determined by the formula: R = (R 10.59 + R 20.59 + . . . + R n0.59 + as) 1.7 (Equation 7-10) where: R = The fire-resistance of the assembly (hours). R 1 , R 2 and R n = The fire-resistance of the individual wythes (hours). as = Coefficient for continuous airspace. Values for R n0.59 for use in Equation 7-10 are given in Table 722.4.1(3). The coefficient for each continuous air-space of 1/2 inch to 3 1/2 inches (12.7 to 89 mm) separating two individual wythes shall be 0.3.
