The Institute for Business & Home Safety (IBHS) today
released information to help determine if snow buildup will be a
problem and when removal is critical.
"Deep snow is deep trouble," said Dr. Tim Reinhold, IBHS
Director of Engineering. "And rain on top of snow can significantly add
to the weight. Even a partial roof collapse can cause extensive damage
to the interior contents of a home or business. When all that snow
comes in, it melts, and can flood the building."
The age of the building is a major factor in the snow load
risk, although snow load designs have not changed much in recent years.
Light metal buildings will typically have less capacity to handle a
high snow load. For flat roofs, the step-down area between roof
sections is a potential source of roof overload because of the tendency
for ice and snow collection.
The best source for determining how much snow load a building
can handle is the design plan. IBHS says most roof designs can handle
at least 20 lbs per square foot. These designs can range from 10 to 20
lbs per square foot in Mid-Atlantic states, and between 40 and 70 lbs
per square foot in New England. IBHS offers these general guidelines to
help estimate the weight of snow:
- Fresh snow: 10-12 inches of new snow is equal to one inch
of water, or 5.2 lbs per square foot of roof space, so you could have 4
feet of new snow before you need to worry.
- Packed snow: 3-5 inches of old snow is equal to one inch of
water, or 5.2 lbs per square foot of roof space, so anything more than
2 feet of old snow could be dangerous.
- The total accumulated weight of two feet of old snow and
two feet of new snow could be as high as 60 lbs per square foot of roof
space, which is getting toward the limits of even the best designed
roof.
- If there's ice, it's much heavier, with one inch equaling
about a foot of fresh snow.
For safe removal that won't endanger you or damage your roof,
consult a roofing contractor.
To help minimize the risks from melting snow, IBHS suggests
keeping attics well ventilated to reduce the risk of ice dams forming.
A warm attic melts snow on the roof, causing water to run down and
refreeze at the roof's edge where it's cooler. An ice buildup blocks
water from draining and forces water under the roof covering and into
the attic or down the inside walls.
Commercial buildings with flat roofs are particularly
vulnerable to water leaks if ice dams clog roof drains. Water can also
find its way inside on sloped roofs along the eaves.
To maintain proper drainage, remove snow from window wells and
all walls. Clear debris from basement drains. Make sure gutters are
clean and stable to ensure proper drainage.
IBHS research shows about $1 of every $5 paid for home and
business property losses in recent years has stemmed from damage due to
freezing weather, snow and water leaks. For more information, visit the
IBHS web site http://www.DisasterSafety.org.
IBHS is an independent, nonprofit, scientific and educational
organization wholly supported by the property insurance industry. The
organization works to reduce the social and economic effects of natural
disasters and other risks to residential and commercial property by
conducting research and advocating improved construction, maintenance
and preparation practices.
Posted 11th March 2008
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