1607.13.2.1 Ordinary roofs, awnings and canopies.
BC § 1607.13.2.1
Ordinary flat, pitched and curved roofs, and awnings and canopies other than of fabric construction supported by a skeleton structure, are permitted to be designed for a reduced uniformly distributed roof live load, Lr , as specified in the following equations or other controlling combinations of loads as specified in Section 1605, whichever produces the greater load effect. In structures such as greenhouses, where special scaffolding is used as a work surface for workers and materials during maintenance and repair operations, a lower roof load than specified in the following equations shall not be used unless approved by the commissioner. Such structures shall be designed for a minimum roof live load of 12 psf (0.58 kN/m 2 ). Lr = LoR1R2 (Equation 16-33) where: 12 ≤ Lr ≤ 20 For SI: Lr = LoR1R2 where: 0.58 ≤ Lr ≤ 0.96 Lo = Unreduced roof live load per square foot (m 2 ) of horizontal projection supported by the member (see Table 1607.1). Lr = Reduced live load per square foot (m 2 ) of horizontal projection supported by the member. The reduction factors R1 and R2 shall be determined as follows: R1 = 1 for At ≤ 200 square feet (18.58 m 2 ) (Equation 16-34) R1 = 1.2 - 0.001At for 200 square feet < At < 600 square feet (Equation 16-35) For SI: 1.2 - 0.011At for 18.58 square meters < At < 55.74 square meters Rt = 0.6 for At ≥ 600 square feet (55.74 m 2 ) (Equation 16-36) where: At = Tributary area (span length multiplied by effective width) in square feet (m 2 ) supported by any structural member, and R2 = 1 for F ≤ 4 (Equation 16-37) R2 = 1.2 - 0.05 F for 4 ≤ F ≤ 12 (Equation 16-38) R2 = 0.6 for F ≥ 12 (Equation 16-39) where: F = For a sloped roof, the number of inches of rise per foot (for SI: F = 0.12 × slope, with slope expressed as a percentage), or for an arch or dome, the rise-to-span ratio multiplied by 32.
