722.3.3 Multi-wythe masonry walls.
BC § 722.3.3
The fire-resistance rating of wall assemblies constructed of multiple wythes of masonry materials shall be permitted to be based on the fire-resistance rating period of each wythe and the continuous airspace between each wythe in accordance with the following formula: RA = (R10.59 + R20.59 + . . . + Rn0.59 + A1 + A2 + . . . An ) 1.7 (Equation 7-7) where: RA = Fire-resistance rating of the assembly (hours). R1 , R2 , . . ., Rn = Fire-resistance rating of wythes for 1, 2, n (hours), respectively. A1 , A 2 , . . ., A n = 0.30, factor for each continuous airspace for 1, 2, . . .n, respectively, having a depth of 1/2 inch (12.7 mm) or more between wythes.
