The roof collapse at a Fred Meyer store Monday has sparked anxiety over the possibility of house roofs collapsing from the weight of snow.
However, structural engineers say the collapse of the 175-by-75-foot section of roof over a Fred Meyer department store, 3215 S. 33rd East, at about 11 a.m. Monday under the weight of nearly 2 feet of snow, is not sufficient reason for everyone to climb on their roofs and start shoveling."People shouldn't get panicked, get out there on their roofs and start filling the hospitals up with broken backs and broken legs," said Larry Reaveley, a structural engineer.
Homes in Salt Lake County are built to withstand 30 pounds of pressure per square foot.
"If we had roofs going down everywhere, we would say our design load has been reached. But when we have an isolated roof failure; that tells me we shouldn't be concerned."
The Fred Meyer store was closed when the roof collapsed, so no one was injured. Officials say a disaster was averted by fire and maintenance workers who recommended the store remain closed.
"You take the load of people that would have been shopping and returning things at 11 a.m. . . . It would have been quite a major catastrophe," Salt Lake County Fire Capt. Max Berry said.
Berry said fire officials were contacted about 4:40 a.m. Monday by a maintenance worker at the store concerned because of a 6-by-15-foot bulge in the ceiling.
Lt. Ted Burke responded and found cracked support trusses in the roof and recommended that the store remain closed.
Three structural engineers interviewed by the Deseret News were not alarmed by the collapse of the Fred Meyer roof. All three said the weekend snow did not have enough moisture in it to reach the 30-pounds-per-square-foot stress limit.
However, if the snow melts and packs down and more snow falls, homeowners may want to start removing snow, Reaveley said.
"This light powder can weigh as little as 10 pounds per square foot of depth," he said. "You can have 2 or 3 feet of light powder and, if your roof has been done right, not have a problem.
Salt Lake County Architect Tom Triptow said it would take 4 feet of the kind of snow we have right now to reach the stress limit for most roofs.
"The type of snow we have now could even get as high as 5 feet without being a serious problem.
"I have over 3 feet of snow on my roof. I'm not going to shovel my roof, and its pretty average construction," Triptow said.
If the snow melts and the roof has poor drainage, there may be a problem, Reaveley said.
"Ice can weigh almost 60 pounds per foot of depth," he said. That's twice the stress limit of most Salt Lake roofs.
"Six inches of pure ice is about all your roof is designed to hold," he said. "If you've got dead flat roofs or your roof isn't draining, then your ice will build up."
People with flat roofs or drainage problems may want to remove snow from their roofs.
Homeowners who want a more definitive answer, should contact a structural engineer.
"Any structural engineer - and there are 40 listed in the phone book - could help."
But don't just dash out on the roof and start wacking away.
"People can ruin their roofs by getting up there and whaling away at them," Reaveley warned.
Often, standing on a ladder and using a broom to brush the powder off will be adequate.