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'If you're worried, then shovel' |
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Wednesday, 31 December 2008 |
About those snow loads on roof
BY CHRIS COWBROUGH
S-E Editor
If home or business owners are worried about increasing snow loads on their roofs, then city of Colville Building Inspec¬tor Bob Cleaver has a tried and true piece of winter advice.
“If people are worried about snow loads, then my recom¬mendation is to shovel it,” Cleaver said on Friday in the wake of the latest snowstorm that dumped an additional six inches to well over a foot of new snow in the Colville valley and surrounding mountains.
This month’s record snowfall on what looks like a winter snowfall pipeline from the North Pacific, was expected to con¬tinue over the weekend.
Cleaver likened the late De¬cember snowfall totals as they relate to roof snow loads as “kind of the in between pe¬riod…there is probably around 24 pounds per square foot (on roofs).”
Until late last week, the snow that had fallen in the Colville valley and surrounding moun¬tains had been dry and light. The Spokane office of the Na¬tional Weather Service was fore¬casting warmer temperatures and accompanying wetter snow.
Building officials like Cleaver recommend keeping an eye not so much on the amount of snow, but on the weight.
At the top of the list of struc¬tures at greatest risk during heavy snowfall are carports and awnings.
On Friday, the awning over the Habitat For Humanity Thrift Store on North Main St. in Colville collapsed under the weight of recent snowfall.
“We have had a wild two weeks (of weather),” Cleaver said. “And it’s still December. If we get a Chinook situation and rain, those snow loads right now could double. That’s when you have problems.”
The veteran building official remembers the winter of 1996 when Colville had more that its share of heavy snowfall. There were several roof failures then, including the collapse of the Colville Junior High School roof.
“This winter looks like another one of those (major snow) win¬ters,” Cleaver said. “We will likely see some failures.”
Homeowners should weigh the risk of personal injury from a roof fall against “peace of mind” that could be gained by remov¬ing snow from a roof.
There are situations where shoveling snow off a roof at home could actually damage a roof. And, in some cases, the weight of a person on a weaker part of a roof could conceivably cause a greater structural problem than not shoveling off the snow.
But there is that home-owner/business-owner caveat.
“If you feel like you should shovel,” Cleaver added, “then my recommendation would be to shovel.”
Before the latest storm last weekend, the National Weather Service indicated that snow on the ground in this area is equivalent to about 1.4 inches of water. Dry has been the by¬word.
But that was expected to change with the arrival of warmer Pacific air and wetter snowfall.
The accumulation of snowfall in the Colville Valley and else¬where around Northeast Wash¬ington means many things to many residents. For owners of buildings/homes with relatively flat-pitched roofs, there are snow load issues.
Failure of buildings can occur when there is improper building design; improper building con¬struction; imbalance of snow load on the roof and failure of one key member causing others to fail as a result of load trans¬fer.
Wood structures will show stress before they fail, unlike metal structures that usually will not. For a wood structure, the following audible and/or visual signs may be noticed prior to failure:
*Creaking or moaning in the building
* Bowing of truss bottom chords or web members.
*Bowing of rafters or purlins
*Bowing of headers or col¬umns
0635…
Volunteers work to make emergency repairs to Thrift Store awning.
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Last Updated ( Wednesday, 07 January 2009 )
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