Is Your Roof Safe From Snow Collapse?
EAGAN, Minn. (WCCO) — With a shovel in hand, Jose Salazar has all he can handle, scraping and heaving away three feet of drifted snow from an Eagan rooftop. He’s supervising one of 10 crews that Sela Roofing has working all around the Twin Cities, dealing with heavy snow and ice dams.
But they’re not alone. Just a few doors away, it’s the same old problem but with a different technique. Crews with Lindus Construction are using a hose blasting 300 degree steam to remove a large ice dam.
“Those ice chunks when picked up they’ve got to be 30 or 40 pounds. So just one piece, imagine how much is really up there,” said James Brandt.
All that weight adds up and often with devastating consequences. So far this season we’ve seen it with the collapse of the Hubert H. Humphrey Metrodome, home of the Minnesota Vikings.
In December, an animal shelter near Baldwin, Wis. lost it’s covered pet run under the weight of deep snow.
Engineering firms say they’re seeing structural collapses affecting both gabled roofs and flat ones.
That’s why beginning in the mid-70s, Minnesota building codes imposed strict standards on building designers and contractors to build structures to withstand extreme snow loads.
“Typically 35 pounds per square foot is the design load, and in northern Minnesota it’s slightly higher,” said Joseph Cain, a structural engineer with the firm Mattson, Macdonald and Young in Minneapolis.
Cain says that’s roughly equivalent to the weight of about 6 feet of snow. However, there are many variables in calculating the safe limits such as the density of the snowpack and its moisture content.
Still, concern is growing over the structural integrity of older structures, including buildings with flat or slightly gabled roofs as well as parking ramps. The concrete structures are not designed to have large piles of snow piled up in concentrated areas.
“When they plow sometimes the snow gets concentrated in large piles which isn’t a good idea. I don’t think they’re typically designed for that,” said Cain.