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    How to Keep Your Roof from Collapsing

    By By Bo Zhang, AccuWeather Staff Writer
    March 14, 2013, 7:42:42 AM EDT

    Winter nightmares aren't just limited to dangerous roads and extreme cold. With heavy snowfall comes the threat of building damages and collapses.


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    According to the Massachusetts Emergency Management Agency (MEMA), in the first 48 hours after the Groundhog Day snowstorm, there were more than 80 collapses and buildings with structural weaknesses reported to MEMA.

    Snow-related building collapses are usually caused by heavy loads of snow on roofs, so this season has been unique because of the extreme weather. Recent rain and sleet made the situation even worse, since the rain could get soaked up by the snow and add even more weight to roofs.

    A cubic foot of dry snow weighs about 6 to 8 pounds, while one cubic foot of packed snow could weigh up to 20 pounds. The same volume of ice can weigh three times this amount.


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    According to a 2008 report from Structure Magazine, causes of snow-related structural problems normally include roof step snow drift, parapet wall snow drift, gable roof snow drift, open air and freezer (uniform loads across the whole roof), sliding snow and ice dams.

    Low-pitched and flat roofs are more vulnerable to snow accumulation; lower roofs are of larger risks as well.

    How to calculate your roof snow load

    • Consult your local permit issuing authority to find the recorded snow load (the maximum snow expected to fall) in your region.
    • Calculate your roof pitch: Divide the "rise" (vertical distance between the peak of the roof and the edge) by the "run" (distance from the peak of your roof to the edge) and convert the fraction to a ratio of 12. (For example, if the rise of your roof is 15 feet, the run is 36 feet, then the pitch = 15 feet / 36 feet = 5:12)
    • Use a calculator like this one. Enter values of your roof and follow the instructions to get your roof snow load.


    How to spot problems with your building

      When you see any of the following problems, call your local building or fire official immediately.
    • Sagging roofs
    • Severe roof leaks
    • Cracked or split wood members
    • Bends or ripples in supports
    • Cracks in walls or masonry
    • Sheared off screws from steel frames
    • Sprinkler heads that have dropped down below ceiling tiles
    • Doors that pop open
    • Doors or windows that are difficult to open
    • Bowed utility pipes or conduit attached at ceiling
    • Creaking, cracking or popping sounds


    How to remove snow from your roof

    • Use a snow rake for pitched roofs.
    • Start from the edge to the peak of the roof.
    • Shave the snow down to 2-3 inches instead of scraping the roof clean; don't damage the shingles.
    • Plastic shovels are better than metal ones (metal tools conduct electricity and damage roofs).
    • Remove large icicles carefully.
    • Wear headgear and goggles.
    • Consider hiring a professional.
    • Have someone outside to protect you.
    • Don't add your weight or the weight of equipment to the roof.
    • Don't use a ladder since ice tends to build up on both the rungs and your shoes.
    • Don't use electric heating devices like heat guns to remove snow and ice.
    • Don't use open-flame devices to remove snow and ice.


    (Reference: Public Safety Advisory On Potential Roof Collapses by Massachusetts Emergency Management Agency)

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