1607.13.2.1 Ordinary Roofs, Awnings and Canopies
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 building official. Such structures shall be designed for a minimum roof live load of 12 psf (0.58 kN/m2).
where: 12 ≤ Lr ≤ 20
For SI: Lr = LoR1R2
where: 0.58 ≤ Lr ≤ 0.96
The reduction factors R1 and R2 shall be determined as follows:
At = Tributary area (span length multiplied by effective width) in square feet (m2) supported by the member, and
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.