Winter is quickly approaching and several areas of the country are already dealing with snow. Our partners at Butler Manufacturing have prepared some helpful suggestions to assist building owners and facility managers deal with severe or heavy snow storms that may occur.
Heavy and/or repeated snow storms can create packed snow and ice such that only a few feet of depth may weigh 50 psf or more, imposing unusual and excessive loads on any building structure. Blowing and drifting snow can easily double these loads and rain on snow can also cause significant load increases. An excessive accumulation of snow can cause a building to be loaded beyond design capacity creating a risk of building damage or even collapse.
Most snow related losses occur at stepped elevations where blowing snow is carried from the roof of a higher building onto the roof of a lower building. Such drifting normally occurs where the buildings are attached. However, drift loads can also form on closely adjacent buildings, over ridges, at valley conditions, behind parapets, next to rooftop units, and on below-eave canopies or overhangs. Post construction changes to the building site, such as the addition of higher buildings or significant tree growth, can cause drifting where none was anticipated. Modifications to the structure, loads added after the original design (such as piping, roof units, hanging heaters, etc.) and prior damage to the structure are other areas of particular concern because they may have significantly reduced the capacity of the building to withstand snow loads.
We recommend that building owners and facility managers be aware of the damage which can occur when excessive snow accumulation is present. Much of the public is unaware of the consequences of allowing snow buildup on their roofs. However, many property insurers are beginning to provide their insureds with information on what to do in the event of a snow emergency, such as advising building owners to activate a snow watch and removal crew to monitor snow depths and to remove excessive accumulations of snow from the roofs.
Building owners should also be advised to keep drains and gutters clear of ice and snow to facilitate melting run-off. Ice and snow build-up can cause excessive loads even without drifts. Building owners should also be aware of warning signs inside the building that may indicate excessive snow accumulation, including the deflection of purlins, the popping of ceiling tiles in drop ceiling, and unusual noises. If any of these situations occur, the building owner or facility manager should contact an Engineer, a construction or roofing professional immediately for assistance.
Buildings are designed to meet historical climatic data as set out in the Building Code; however, the extreme weather events we are seeing more frequently are not necessarily covered by these design requirements. Consistent monitoring of your building's roof, along with proper maintenance and preventive measures, can help you avoid incidents and potentially extend the overall life of your roof.