(02/23/2010)
Submitted by Brandy Brabham
WVU Extension Agent
354-6332 or 927-0975

Although this week started out rainy and relatively warm, the recent snowstorms have had residents focusing on road conditions, school closings and other challenges. But most people don't realize how damaging excessive snow loads can be to their homes and farm and business structures.

However, recent roof collapses in more heavily hit areas are drawing attention to this problem.

Roofs fail for a number of reasons, said Joshua Faulkner, agricultural engineering specialist with the West Virginia University Extension Service.

If the actual snow load on the roof is greater than the design load, he said, the roof may collapse. Improper building design and faulty construction can also result in failure. Older buildings that have been subjected to decay or damage are also at risk. In addition, buildings are typically only designed to hold the design loads for about a month before structural fatigue weakens the roof and collapse can occur.

If you believe too much snow is on your building, the best thing to do is to remove it.

Shovels, snow rakes and brooms work well. Faulkner cautioned that removing snow can be a potentially dangerous task and should only be performed using the utmost caution and safety procedures. Be aware that ice is often under the snow. Take care to look for and avoid any overhead electrical lines.

For larger buildings, he said, you should consult with properly trained individuals. "Removing the snow in an unbalanced manner can result in unequal point loads," he explained.

Wood buildings often exhibit certain signs before they fail. "Sounds such as creaking, cracking and moaning of building components can indicate potential failure. Any bowing of structural members should also be viewed as a warning sign. If you notice any of these signs, safely and quickly evacuate the building," the WVU Extension engineer explained.

If you are wondering why this is such a problem this year, Faulkner has been answering the question by first saying: "All snow is not created equal."

Snow can have a wide range of moisture contents, he said, and this moisture content directly controls the weight the snow.

"Dry snow—that light fluffy powdery stuff—is much lighter than dense, heavy 'wet' snow. For example, two feet of a typical 'dry' snow will exert a load of just under 10 pounds per square foot on a flat surface, while the same depth of a 'wet' snow can exert over 40 pounds per square foot," he said.

Much of the snow West Virginia recently received was on the "wet" end of the spectrum.

In those areas that received more than three feet of snow, the maximum estimated ground snow loads approached 70 pounds per square foot.

The actual snow load on a roof is often less than the load on the ground.

"That's because winter winds can blow some of the snow off of the building. But if snow drifts occur on the roof," Faulkner said, "loads can significantly increase. However, typically, as roof slope increases, the snow load decreases because snow tends to slide off instead of build up."

Can you protect your home or business before the snow falls? Faulkner recommended that every fall and before big storms, make sure all gutters and downspouts can flow freely to help prevent ice buildup and properly drain melting snow off of roofs.

For more information about snow, ice and roof problems, check www.extension.org


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