Snow Removal Strategies of Lightweight, Flat Roof Structures

This paper provides guidance to engineers, property owners, property managers, and contractors on the mitigation of damage to lightweight, flat (or low slope) roof structures by snow removal. The objectives are to minimize large deflection, prevent blocked drainage paths, minimize snow-induced ponding, and most importantly, to prevent the collapse of roof structures caused by overload due to snow. The structures most susceptible to overload are lightweight, flat roof, commercial structures, such as "Big Box" stores, warehouses, recreation centers, and shopping malls. These structures commonly have low permissible snow load to dead load ratios making them sensitive to extreme snow loads. In February 2010, there were three successive snowstorms extending from Washington, DC to New York, New York that challenged snow removal efforts. Each storm was a significant event and together in quick succession, these storms caused the collapse of roof structures throughout the region. The collapse of roof structures and the forecast for significant accumulation after the first storm prompted property owners and managers to take precautions to protect their property from damage. Conditions and events motivated the development of these snow removal guidelines to protect against overload. Factors influencing a successful snow removal strategy include the amount of snowfall (i.e., depth of snow, unit weight of snow, and drifting snow), design capacity and condition of the roof structure, potential to exceed the design requirements and/or code specified requirements, size of the roof structure, safety of the snow removal crews, economic aspects of snow removal, etc. This paper considers strategies for snow removal, such as taking no action, removing a uniform depth of snow throughout the roof structure, removing channels of snow from the field of the roof, or a combination. The methodology presented may also be adapted to roof structures undergoing rehabilitation, such as re-roofing.