A heavy snowstorm or blizzard that can accumulate several inches of snow quickly can be trouble for a business, especially on the roof. Should there then be rain, on top of snow, this can significantly add to the weight and be in danger of collapse.
Even a partial roof collapse can cause extensive damage to the interior contents of a business. When the snow comes in, it melts and can cause flooding or water damage inside the building.
To avoid a possible roof collapse under heavy snow, it is important to know how to estimate the weight of the snow and ice on the roof and when to remove it. The Institute for Business & Home Safety (IBHS) offers general guidelines to help estimate the weight of snow on commercial roofs:
- Fresh snow: 10-12 inches of new snow is equal to one inch of water, or about 5 pounds per square foot of roof space.
- Packed snow is heavier than new snow and 3-5 inches of old snow is equal to one inch of water or about 5 pounds per square foot of roof space.
- Ice is also heavier than snow. One inch of ice equals about a foot of fresh snow.
- The total amount of accumulated snow and ice is what matters in evaluating snow load risk. For example, the accumulated weight of two feet of old snow and two feet of new snow could be as high as 60 pounds per square foot of roof space, which may stress the limits of even the best designed roof.
If you are in the “danger zone” according to chart above or if the loads you estimate based on the thickness of the various types of snow and ice exceed 20-25 pounds per square foot, you
should consider having the snow removed from your roof by a professional.
Visit IBHS for more information and a diagram on how to estimate the roof load and when to remove snow.
NOTICE: This information is provided solely as an insurance risk management tool. It is provided with the understanding that the member insurance companies of the Utica National Insurance Group are not providing legal advice, risk management advice, or any other professional services or advice. Utica National shall have no liability to any person or entity with respect to any loss or damages alleged to have been caused, directly or indirectly, by the use of this information. You are encouraged to consult an attorney or other professional for advice on these issues.