Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 16 - Structural Design
Section 1607 - LIVE LOADS
Subsection 1607.11 - Roof loads
Current through Register 1531, September 27, 2024
The structural supports of roofs and marquees shall be designed to resist wind and, where applicable, snow and earthquake loads, in addition to the dead load of construction and the appropriate live loads as prescribed in this section, or as set forth in Table 1607.1. The live loads acting on a sloping surface shall be assumed to act vertically on the horizontal projection of that surface.
1607.11.1 Distribution of roof loads. Where uniform roof live loads are reduced to less than 20 psf (0.96 kN/m2) in accordance with Section 1607.11.2.1 and are applied to the design of structural members arranged so as to create continuity, the reduced roof live load shall be applied to adjacent spans or to alternate spans, whichever produces the most unfavorable load effect. See Section 1607.11.2 for reductions in minimum roof live loads and Section 7.5 of ASCE 7 for partial snow loading.
1607.11.2 Reduction in roof live loads. The minimum uniformly distributed live loads of roofs and marquees, Lo, in Table 1607.1 are permitted to be reduced in accordance with Section 1607.11.2.1 or 1607.11.2.2.
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).
| Lr = Lo R1R2 | (Equation 16-25) |
where: 12 <= Lr <= 20
For SI: Lr = LoR1R2
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 (18.58 m2) | (Equation 16-26) |
| R1 = 1.2 - 0.001At for 200 square feet < At < 600 square feet | (Equation 16-27) |
For SI: 1.2 - 0.011At for 18.58 square meters < At < 55.74 square meters
| R1 = 0.6 for At >= 600 square feet (55.74 m2) | (Equation 16-28) |
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 16-29) |
| R2 = 1.2 - 0.05 F for 4 < F < 12 | (Equation 16-30) |
| R2 = 0.6 for F >= 12 | (Equation 16-31) |
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.
1607.11.3 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.
1607.11.4 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.
