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Roofs Should Hold Normal Snow Load

Don’t be too hasty when deciding to shovel snow off your roof.

Don’t rush to shovel snow off your roof.

“Most roofs are designed to handle the snow load of a typical winter,” North Dakota State University Extension Service agricultural engineer Ken Hellevang says. “Just because one roof has gone down doesn’t mean every roof in the area is in danger. The collapse may have been a case of poor workmanship or design, unusual amounts of snow or some other special circumstance.""

Hellevang says most house roofs in eastern and northern North Dakota should hold 30 to 40 pounds of snow per square foot. In the southwestern part of the state, where snowfall typically is lighter, roofs are built to hold less - about 30 pounds per square foot.

“Agricultural buildings usually aren’t designed to those same standards,” Hellevang says. “That’s because the risk of damage or injury from collapse is considered to be lower.”

Agricultural buildings should carry 24 to 34 pounds of snow per square foot, depending on location. Agricultural buildings normally are not required to be built to carry a specified snow load and may have been built for a lighter snow load.

Also, snow load standards may not have been in place when older homes and buildings were erected, but if those buildings have withstood the test of time, they'll probably withstand a normal winter’s snow load, Hellevang says

Determining if the snow load on your roof is excessive can be difficult.

“The weight of snow varies greatly,” Hellevang says. “Light, fluffy snow may only weigh about 7 pounds per cubic foot. More average snow may weigh 15 pounds per cubic foot, and drifted, compacted snow may weigh 20 pounds or more.” Ice buildup also adds weight rapidly.

He urges people to monitor the roof for deep drifts caused by surrounding buildings or trees. Roofs that have more than one level often accumulate deep snowdrifts, but those roofs should have been built to carry that added load. If the roof has more than a couple of feet of compacted snow on it, the load may be excessive.

You can inspect the rafters and trusses, and if they are bending downward or flexing to the side, the roof is in danger.

Unless you can get a recommendation from an engineer or building official, the decision to shovel off a roof will be based on an educated guess, Hellevang says.

He recommends you check your insurance policy because failure due to snow may not be covered on agricultural buildings without a purchased rider.

If you do decide to shovel off your roof, remember that snow and ice can make the job dangerous. Agricultural buildings with metal roofs can be especially treacherous, and power lines can be an added hazard.

“You also can damage your roof,” Hellevang says. “Cold temperatures make shingles brittle, so they break easier. You’re also more likely to remove many of the little pebbles from the surface of the shingles, shortening the life of your roof.”

NDSU Agriculture Communication

Source:Ken Hellevang, (701) 231-7243, kenneth.hellevang@ndsu.edu
Editor:Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu
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