Snow Load Safety Guidance for Roofs

UTICA NATIONAL RISK MANAGEMENT ALERT

This handout summarizes warning signs of overstress conditions during a snow event, key safety issues, and risks a snow event poses to buildings, and what to do after a snow event, including tips for removing snow from roofs during winter weather. The information is adapted from the FEMA Snow Load Safety Guidance, developed by the U.S. Federal Emergency Management Administration (FEMA). The handout does not address preventative measures to take before snow season.

Warning Signs of Overstress Conditions During a Snow Event

Overstressed roofs typically display some warning signs. Wood and steel structures may show noticeable signs of excessive ceiling or roof sagging before failure. The following warning signs are common in wood-, metal-, and steel-constructed buildings:

• Sagging ceiling tiles or boards, ceiling boards falling out of the ceiling grid, and/or sagging sprinkler lines and sprinklers
• Sprinklers deflecting below suspended ceilings
• Popping, cracking, or creaking noises
• Sagging roof members, including metal decking or plywood sheathing
• Bowing of truss bottom chords or web members
• Doors and/or windows that can no longer be opened or closed
• Cracked or split wood members
• Cracks in walls or masonry
• Severe roof leaks
• Excessive accumulation of water at non-drainage locations on low slope roofs

If any of these warning signs are observed, the building should be promptly evacuated and a local building authority and/or a qualified design professional should be contacted to perform a detailed structural inspection.

Key Safety Issues and Risks

Snow accumulation in excess of building design conditions can result in structural failure and possible collapse. Structural failure due to roof snow loads may be linked to several possible causes including, but not limited to, the following:

Unbalanced snow load from drifting and sliding snow. When snow accumulates at different depths in different locations on a roof, it results in high and concentrated snow loads that can potentially overload the roof structure.

Rain-on-snow load. Heavy rainfall on top of snow may cause snow to melt and become further saturated, significantly increasing the load on the roof structure.

Snow melt between snow events. If the roof drainage system is blocked, improperly designed, or improperly maintained, ice dams may form, which creates a concentrated load at the eaves and reduces the ability of sloped roofs to shed snow. On flat or low slope roof systems, snow melt may accumulate in low areas on roofs, creating a concentrated load.

Roof Geometry. Simple roofs with steep slopes shed snow most easily. Roofs with geometric irregularities and obstructions collect snow drifts in an unbalanced pattern. These roof geometries include flat roofs with parapets, stepped roofs, saw-tooth roofs, and roofs with obstructions, such as equipment or chimneys.

What to Do After a Snow Event

After a snow event, snow removal may be in order. To determine whether snow removal is necessary, one may enlist valuable resources, such as a local building authority and/or a qualified design professional, who is familiar with the snow conditions of the region and the design capacities of local buildings per the building code. If it is determined that the snow should be removed, snow removal should only be performed by qualified individuals as snow removal is a dangerous activity.

The qualified individual should follow necessary protocols for safe snow removal to minimize risk of personal injury and lower the potential for damaging the roof covering during the snow removal process. If at any time there is concern that snow loads may cause a collapse of the roof structure, cease all removal activity and evacuate the building.

If subsequent snow events are anticipated, removing snow from the roof will minimize the risk of accumulating snow causing structural damage. One benefit of immediate snow removal is that the effort required to remove the snow from the rooftop is reduced.

Safety Measures for Snow Removal

Below are some safety measures to take during snow removal to minimize risk of personal injury.

• Any roof snow removal should be conducted following proper Occupational Safety and Health Administration (OSHA) protocol for work on rooftops. Use fall protection systems, such as fall arrest harnesses, where applicable.
• Always have someone below the roof to keep foot traffic away from locations where falling snow or ice could cause injuries.
• Ensure someone confirms that the area below the removal site is free of equipment that could be damaged by falling snow or ice.
• Whenever snow is being removed from a roof, be careful of dislodged icicles. An icicle falling from a short height can still cause damage or injury.
• When using a non-metallic snow rake, be aware that roof snow can slide at any moment. Keep a safe distance away from the eave to remain outside of the sliding range.
• Buried skylights pose a high risk to workers on a roof removing snow. Properly mark this hazard as well as other rooftop hazards.

Methods of Snow Removal

Below are some recommended methods of snow removal that allow the qualified individual to remove snow safely and minimize risk of personal injury and property damage.

• Removing snow completely from a roof surface can result in serious damage to the roof covering and possibly lead to leaks and additional damage. At least a couple of inches of snow should be left on the roof.
• Do not use mechanical snow removal equipment. The risk of damaging the roof membrane or other rooftop items outweighs the advantage of speed.
• Do not use sharp tools, such as picks, to remove snow. Use plastic rather than metal shovels.
• Remove drifted snow first at building elevation changes, parapets, and around equipment.
• Once drifted snow has been removed, start remaining snow removal from the center portion of the roof.
• Remove snow in the direction of primary structural members. This will prevent unbalanced snow loading.
• Do not pile snow in one area of the roof during removal.
• Dispose of removed snow in designated areas on the ground but do not block drainage grates.
• Keep snow away from building exits, fire escapes, drain downspouts, ventilation openings, and equipment.
• If possible, remove snow starting at the ridge (i.e., peak) and moving toward the eave (i.e., outer edge) for gable and sloped roofs.
• In some cases, a long-handled, non-metallic snow rake can be used from the ground, thereby reducing risk. Metal snow rakes can damage roofing materials and pose an electrocution risk and should be avoided.
• It is recommended that a quick inspection of the structure be performed after a large snow event.
• Where snow removal was necessary, the roofing material should be inspected for any signs of damage as soon as possible.

OSHA has published additional guidance on removing snow from rooftops and other elevated surfaces. The guidance Hazard Alert, "Falls and Other Hazards to Workers Removing Snow from Rooftops and Other Elevated Surfaces," is available from the OSHA website, www.osha.gov.

CH-45-10  |  8/14/19  |  Copyright © 2019, ISO Services, Inc.
The information contained in this publication was obtained from sources believed to be reliable. ISO Services, Inc., its companies and employees make no guarantee of results and assume no liability in connection with either the information herein contained or the safety suggestions herein made. Moreover, it cannot be assumed that every acceptable safety procedure is contained herein or that abnormal or unusual circumstances may not warrant or require further or additional procedure.