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November 15, 2017

Snow On Your Commercial Roof: How Much Is Too Much?

As the seasons change, new weather concerns for your roof will arise. With winter around the corner, you should be aware of the impact – and potential problems – that snow and ice can bring to your roof.

A commercial roof is a complex structure that – in addition to the roofing membrane on the surface and the roof deck – can include layers of insulation, thermal barriers and cover boards, and structural components like beams, trusses, and purlins.

fema snow weight on flat commercial roofsFEMA, in its Snow Load Safety Guide, claims that the weight of one foot of fresh snow can range from three pounds per square foot for light, dry snow to 21 pounds per square foot for wet, heavy snow. Ice is much denser and considerably heavier than even wet heavy snow. An inch of ice weighs just under five pounds per square foot; one foot of ice weighs as much as 57 pounds per square foot. One hundred square feet of foot-thick ice (a relatively small 10-foot by 10-foot area) equals 5,700 pounds. Freeze and thaw cycles can turn relatively harmless amounts of rooftop snow into dangerous amounts of ice.

Every winter seemingly brings stories of building collapses due to snow and ice accumulation. Structural problems caused by too much weight on the roof may show up as signs of stress inside, like jammed doors and windows, or cracks in a wall or ceiling.

If there are more than six inches of packed snow on your roof, you should remove it. Use a snow rake (not a shovel) and leave two to three inches of snow on the roof instead of scraping it to the surface, which can damage the roof membrane. If you’re not comfortable taking care of this yourself, hire a professional.

There is a positive of snow on the roof. If the snow does not reach dangerous amounts, then it can be an added layer of insulation for your roof, which could lower your energy bill.

Of course, when spring does roll around, you should check for signs of damage and ensure that water is able to flow properly off the roof.

Knowing the affects the snow can have on your roof will help you be prepared for the winter.


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