In this article, structural engineer, Mark Duckett, P.E. discusses roof failures associated with snow loads. Topics of discussion include reasonable loads that roofs are designed to support and the role of a forensic expert in determining the cause of failure.
Falling Snow & Collapsing Roofs
Investigating Snow Related Roof Collapses
Roofs are designed to support reasonably anticipated dead and live loads and those loads are quantified by Building Codes. Dead loads represent the self weight of the system while live loads are the loads imposed upon those systems; typically by water, wind and/or snow. Roof snow loads, in particular, can sometimes exceed design load levels in cases where snow accumulates; deep accumulation of snow on a roof can result in overloading or collapse of a roof system. Flat roofs are particularly vulnerable to snow accumulation, as are areas behind high parapets or other roof projections such as roof-mounted mechanical equipment. According to FM Global studies, snow load is the most serious cause of roof collapse.
Some building roofs fail under snow loads that a properly designed and maintained roof should have been able to sustain without collapsing. If structural supports were allowed to deteriorate or were modified, or if alterations to a building caused unusually high drifting, those actions may cause premature failures. When large accumulations of snow are forecast, snow can be removed or reduced to prevent structural overloading.
If a building’s roof does collapse, the owner should immediately safeguard the premises and restrict access to the building. Next, as a first step towards repairing the roof and recovering damages resulting from the collapse, they should contact their insurance carrier and arrange for an engineering expert to evaluate the stability of the remaining structure. That expert, or team of experts, can investigate the failure to determine cause and mode of the collapse.
Robson Forensic engineers and architects are frequently engaged to investigate roof failures. Our experienced forensic experts can help to determine:
If the roof failure was caused by an excessive snow load (ie, exceeding design load). Further, if it was caused by an excessive snow load, our experts can determine whether the failure occurred instantaneously, during the events of a single storm, or whether it was due to a progressive accumulation over a winter season that should have been observed and addressed by a reasonably attentive property owner.
Whether or not that failure was the result of an inadequate design.
If the roof collapse was the result of renovations/modifications to the building wherein those changes produced deeper snow (drifts) on parts of the roof not intended to support those loads.
If the collapse of the roof system was a result due to an error in construction.
Whether or not alterations to or improper maintenance of the roof structure, caused the collapse.
Whether reasonable efforts had been made to remove snow, reduce snow loads on the roof to prevent overloading and collapse.
It takes a construction professional to determine these factors, and it is best that an engineer or architect be on site soon after the collapse, although determinations can be made post cleanup based on photographic and other evidence.
Structural Failure Investigations
The engineers & architects at Robson Forensic are frequently retained to investigate structural failures to determine the cause of failure and extent of damage. Our experts are located throughout the country and perform investigations in all fifty states.
Architects are experts in the built environment, from design and construction to inspection and maintenance. The architects at Robson Forensic provide investigations into a broad range of claims involving the design, construction, and maintenance of buildings and outdoor environments, including building failure issues.
For more information visit our Architectural practice page.
Civil/Structural Engineering Experts
Civil engineers design and build many of the structures we encounter on a daily basis. Engineering experts specialize in determining the cause of structural failures and evaluating the integrity of compromised structures.
For more information visit our Civil Engineering practice page.
Using both government and private weather records, our expert meteorological reports are written specifically to the details of your case to provide insight on snowfall rates and accumulation.
For more information visit our Meteorology practice page.