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Snow-covered roofs: Safety considerations

By Kate Donnelly
Jan 26, 2016

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Snow-covered roofs: Safety considerations We all know the damage snow can do to our parking lots, but it's easy to overlook the impact it can have on our roofs. On the less serious side of things, snow accumulation up there can affect the efficiency of our air filtration and circulation systems, and on the more serious side, can result in roof collapse. Removing snow from such a height is no easy task, either, and many maintenance staff are unaware of the procedures for safe snow removal.

Determine your snow limit

Each building has a certain amount of snow that it can safely handle. Sometimes this weight limit can be easily found in the building plans, but if not, you should enlist the help of a structural engineer who can determine the max weight. FacilitiesNet noted that sometimes the safe snow load amount could be 50 percent of the roof's original design snow load, and urges managers to keep in mind that snow that has been somewhat thawed and then refrozen is heavier than freshly fallen snow, with refrozen snow weighing in at 40 to 60 pounds per cubic foot compared to fresh snow's weight of 10 to 20 pounds per cubic foot.

When measuring snow loads, the site also reminds managers that measuring that depth of the snow is not representative of the snow's weight. Additionally, sometimes the snow can seem shallower than it really is. To accurately measure the weight of snow, you should take 12-inch square samples.

Identify hazards

Other factors can influence how susceptible your roof is to collapse or damage caused by snow. Consider any equipment or systems that have been added to your roof, such as solar panels and HVAC systems, which contribute extra weight. Also watch out for ice building up in gutters and drains, which can also help cause a collapse. The insurance company Travelers noted that two specific types of roofs are at risk for collapse and damage due to snow: wood bowstring truss roofs and structural standing-seam metal roofs. If you have the truss roof, be aware that this roof type is historically prone to failure, because of the deterioration of the truss, and have a structural engineer regularly inspect the premises. Standing-seam metal roofs that were built prior to 2000 are also prone to collapse, so have them evaluated as well.

Develop a safe snow removal plan

There isn't just risk from collapse, but risk of worker injury during the snow removal process. In the past decade, the Occupational Safety & Health Administration has investigated 16 serious injuries or fatalities from workers removing snow and ice from roofs and other building structures like decks, and warns that workers may fall from ladders or roof edges or through skylights. To keep workers safe, OSHA recommended that you use snow removal methods that don't involve workers going onto the roof whenever possible, be aware of the added weight from workers and removal equipment compared to the load limit of the roof, ensure that workers use aerial lifts and ladders safely, require that workers wear fall protection equipment and clearly mark trip hazards.

Safer ways of removing snow from the roof include using ladders to distribute de-icing chemicals and materials, and using drag lines or snow rakes from the ground. However, these methods have their own risks and also require careful attention. When using a snow rake, workers should make sure they are removing the snow uniformly off the roof in small amounts and do not make piles of snow. If workers are unable to safely remove snow, hire a private company to take care of it for you.

Be aware of warning signs

Be on the lookout for signs that the roof is overloaded and may collapse. These include:

  • Cracked or broken windows
  • Cracking of structural supports, exterior structures and interior walls and ceilings
  • Dropped ceiling tiles and drooping sprinkler heads
  • Serious roof leaks
  • Windows and doors that do not open or close correctly
  • Loud popping noises coming from the building structure and supports

Travelers advised that if you see any of these signs, immediately contact a structural engineer to perform an inspection. Depending on the risk level and severity of the situation, you may need to evacuate the building, shutdown gas mains and shutdown and drain sprinkler systems.
These tips will help make sure that your roof is stable, strong and safe this winter.

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