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Under pressure: Can your roof handle the snow load?

Thursday, January 14, 2010

(Sentinel photo by Renee Nyhof) Bill Anthony shovels snow off a roof in Le Mars. With heavy snowfall this winter and plenty of drifting, people's roofs might be under too much pressure. Cleaning snow off roofs can be important, but requires caution.
Last week, several members of the Plymouth County Board of Supervisors and some volunteers were on top of the courthouse, scooping snow to the ground from 6-foot drifts.

They cleared the flat roof section of the courthouse.

"(Supervisor) Don Kass estimated we moved probably 3 or 4 tons of snow," Supervisor Craig Anderson said, explaining they moved the snow to eliminate possible damage to the building.

They aren't the only brave souls who have been shoveling and snowblowing the roofs of houses and other buildings around town.

With more than 2 feet of snow falling on Le Mars in the last month and a half, plus wind that built up large drifts, several roofs in northwest Iowa, like that of the Hinton Community School's technology room, have collapsed under the weight.

Now people are taking precautions to make sure their roof doesn't fall flat.

"Usually Mother Nature takes its course, but this year it hasn't been working that way," said Bryan Nohava, owner of Nohava Construction in Le Mars.

In most cases, 6 or 7 inches of snow falls, then melts, he said.

"But we've got 2 feet of snow and with this massive amount of winds we've had we've got huge drifts. We've had an extreme amount of snow and extreme duration of freezing temperatures," Nohava said. "To melt a 10-foot drift on a building is going to take a lot of heat."

Since it's only mid-January, the snow could sit on roofs for another two months, he said.

In talking to engineers, Nohava has heard 18-20 inches of snow can max out a roof's snow load.

"That's when you've got to start looking at getting it off the roof," he said.

Nohava has seen 10-15 foot drifts on roofs around Le Mars. The average, he said, is 3-5 feet.

With this week's warmer temperatures, drifts might look smaller but they might be just as dangerous.

According to an online report by Zurich Corporation Risk Engineering in Illinois, 1 foot of wet snow can weigh 21 pounds per cubic foot, compared to 1 foot of dry snow, which weighs about 3 pounds per cubic foot.

What are some warning signs a roof is bearing too much weight?

Watch for sagging rafters, Nohava said, and listen to your building for unusual noises.

"Go in your building when it's quiet," Nohava said. "If you start hearing some popping noises, creaking noises, something out of the ordinary, check into it."

Zurich Corporation's report also suggests watching for doors that pop open or windows that are difficult to open, bowed utility pipes attached to the ceiling and sprinkler heads pushed down below ceiling tiles.

Nohava said if people choose to remove the snow from their roof on their own, their first priority should be safety.

"The biggest thing is use a lot of caution so you don't get hurt," Nohava said.

For homes with peaked roofs, Nohava recommended using a snow rake.

Snow rakes are specially designed shovels with extendable handles used to pull snow down off a roof.

For flat roofs, Nohava uses shovels and wheelbarrows.

People using equipment like snowblowers to clean flat roofs should be careful not to have too heavy equipment in one area because that extra weight could collapse the roof, Nohava said.

When cleaning a roof, people should be careful not too scrape down too close to the roof itself.

"Try to leave an inch or two so you're not damaging structures such as shingles or any sort of membrane," Nohava said. "You can do a lot of damage."

If it's a house roof, keep the gutters clean and cleared out, he added.

"That's where most of the issues are going to start," Nohava said.

People should also keep downspouts clear so water from melting snow will flow freely, according to the report from Zurich Corporation.

With as much snow as Le Mars has seen this season, there are still a few months of winter to go.

"Usually we get most of our snow in March, so in my opinion we're not out of the woods by a long shot," Nohava said. "But one nice thing about a March blizzard is about two weeks later it's gone."

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