Inland Northwest residents who recall heavy snows of years past may be looking nervously at their roofs and wondering “How much is too much?”
While the strength of a roof depends on many factors - the era it was built, the load it was designed to handle and how well it has been maintained - the short answer probably is: Don’t worry yet.
Jim Manson, Spokane County buildings director, said homes in Spokane built since 1974 are required to have roofs that hold at least 30 pounds per square foot. Houses built in higher elevations may have roofs that hold twice that weight or even more.
Thirty pounds per square foot is about 5 feet of continuously falling snow, Manson estimated. But snow gets heavier with melting, drifting and compacting.
Ice that is left over from the November sleet storm or that has accumulated from a cycle of thawing and refreezing also is much heavier. Rick Ulveling, a building inspector for the Idaho Department of Labor and Industrial Services, estimates that the weight of 1 inch of ice equals 10 inches of snow.
Roofs of homes built before 1974, when the Uniform Building Code went into effect, might be designed to hold less weight, Manson said. But it’s still not a good idea to climb onto a roof and shovel it.
That’s dangerous, and you could do more harm than good by dislodging or damaging shingles, causing the roof to leak later.
For homeowners who are worried about snow buildup, Manson suggests attaching a board to a long pole to form a T, then pulling snow off the eaves while standing on the ground.
Pulling snow off ice dams will cut down on the ice buildup, he added. But don’t whack at the ice with a pole or a shovel. That can damage the roof.
If the snow continues or if rain falls on top of the snow, that may be the time to consider clearing the roof. Snow acts as a sponge, soaking up rainwater and adding extra weight to the roof, Ulveling said.
Look for signs of stress, such as a bowing in the roof, Manson said. Flat roofs are more likely to be at risk because snow doesn’t fall or blow off them as easily.
Be careful whom you hire to clear a roof, he added. If they start whacking at the snow and ice with shovels, they may not know what they’re doing.
And putting several people on a roof at one time can place more weight on the structure than any snow buildup will.
Roofs on some carports and some other buildings in Kootenai County have collapsed since the ice storm. But in some cases, carport roofs gave way because people were on the roof shoveling, Ulveling said.
, DataTimes ILLUSTRATION: Graphic: How ice dams form
The following fields overflowed: BYLINE = Jim Camden Staff writer Staff writer Ken Olsen contributed to this report.
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