Roof Live Loads for Low-Slope Roofs

Abstract

Efficient structural design demands qualitative understanding and statistical characterization of live loads. While live loads have been the subject of extensive study for office and residential buildings, roof live loads have seen little attention. The design of unoccupied low-slope roofs may be governed by roof live loads—loads that are caused by rooftop maintenance, rooftop appurtenances, and inspection. These roof live loads are treated coarsely in national design specifications. In ASCE 7-22, they are prescribed as an equivalent uniform distributed load with no basis provided for the value. Furthermore, the source of roof live loads has never been comprehensively studied. This paper seeks to understand the root causes of roof live loads on low-slope roofs while comparing treatments around the world. As no live load model for roof live loads exists, development of a stochastic model for roof live loads began with the widely-accepted live load model for office buildings. This model is assessed for its sensitivity to the sustained load, transient load, and temporal constants. In general, the model is most sensitive to the standard deviation of the transient load. A questionnaire was developed and administered to survey building managers, engineers, and building maintenance technicians. With these results, and using the calibrated live load model, roof live loads are modeled probabilistically.