SECTION 1607 LIVE LOADS

1607.11.2 Reduction in roof live loads. The minimum uniformly distributed roof live loads, Lo in Table 1607.1 are permitted to be reduced according to the following provisions.

1607.11.2.1 Flat, pitched and curved roofs. Ordinary flat, pitched and curved roofs are permitted to be designed for a reduced roof live load as specified in the following equation or other controlling combinations of loads in Section 1605, whichever produces the greater load. In structures 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 equation shall not be used unless approved by the building official. Greenhouses shall be designed for a minimum roof live load of 12 psf (0.58 kN/m2).

Lr = LoR1R2                     (Equation 16-27) 

where: 12 ≤ Lr ≤ 20

For SI: Lr = Lo R1R2

where: 0.58 ≤ Lr ≤ 0.96

Lr = Reduced live load per square foot (m2) of horizontal projection in pounds per square foot (kN/m2). The reduction factors R1 and R2 shall be determined as follows:

R1  =  1 for At ≤ 200 square feet (18.58m2)      (Equation 16-28)

R1  =  1.2 – 0.001At for 200 square feet <At < 600 square feet   (Equation 16-29)

For SI: 1.2 – 0.011At for 18.58 square meters < At < 55.74 square meters

          R1  =  0.6 for At > 600 square feet (55.74m2)    (Equation 16-30)  

where:

At  = Tributary area (span length multiplied by effective width) in square feet (m2) supported by any structural       member, and

R2  = 1 for F≤ 4 (Equation 16-31)

R2  = 1.2 – 0.05 F for 4 < F< 12 (Equation 16-32)

R2  = 0.6 for F > 12 (Equation 16-33)

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.

1607.11.2.2 Special-purpose roofs. Roofs used for promenade purposes, roof gardens, assembly purposes or other special purposes shall be designed for a minimum live load as required in Table 1607.1. Such roof live loads are permitted to be reduced in accordance with 1607.9.

1607.11.2.3 Landscaped roofs. Where roofs are to be landscaped, the uniform design live load in the land­scaped area shall be 20 psf (0.958 kN/m2). The weight of the landscaping materials shall be considered as dead load and shall be computed on the basis of saturation of the soil.

1607.11.2.4 Awnings and canopies. Awnings and canopies shall be designed for uniform live loads as required in Table 1607.1 as well as for snow loads and wind loads as specified in Sections 1608 and 1609.

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