722.2.1.2.1 Two or more wythes.
BC § 722.2.1.2.1
The fire-resistance rating for wall panels consisting of two or more wythes shall be permitted to be determined by the formula: R = (R 10.59 + R 20.59 + . . . + R n0.59 )1.7 (Equation 7-4) where: R = The fire endurance of the assembly, minutes. R 1 , R 2 , and R n = The fire endurances of the individual wythes, minutes. Values of R n0.59 for use in Equation 7-4 are given in Table 722.2.1.2(1). Calculated fire-resistance ratings are shown in Table 722.2.1.2(2). Table 722.2.1.2(1)Values of Rn0.59 for Use in Equation 7-4 Type of MaterialThickness of Material (inches)1 1/222 1/233 1/244 1/255 1/266 1/27Type of MaterialThickness of Material (inches)1 1/222 1/233 1/244 1/255 1/266 1/27Siliceous aggregate concrete5.36.58.19.511.313.014.916.918.820.722.825.1Carbonate aggregate concrete5.57.18.910.412.014.016.218.120.321.924.727.2 cSand-lightweight concrete6.58.210.512.815.518.120.723.326.0 cNote cNote cNote cLightweight concrete6.68.811.213.716.519.121.924.727.8 cNote cNote cNote cInsulating concrete a9.313.316.618.323.126.5 cNote cNote cNote cNote cNote cNote cAirspace b–––––––––––– For SI: 1 inch = 25.4 mm, 1 pound per cubic foot = 16.02 kg/m 3 . a. Dry unit weight of 35 pcf or less and consisting of cellular, perlite or vermiculite concrete. b. The R n0.59 value for one 1/2" to 3 1/2" airspace is 3.3. The R n0.59 value for two 1/2" to 3 1/2" airspaces is 6.7. c. The fire-resistance rating for this thickness exceeds 4 hours. Table 722.2.1.2(2)Fire-resistance Ratings Based on R0.59 Ra, MinutesR0.596012018024011.2016.8521.4125.37 a. Based on Equation 7-4.
