By Joshua Faulkner
WVU Extension Service Agricultural Engineering Specialist
The recent snowstorms have impacted residents statewide in numerous ways. While focusing
on the road conditions, school closings, and other challenges, we often forget
about how damaging excessive snow loads can be to our home and farm structures.
A number of recent roof collapses in the more heavily hit areas draw attention
to this issue.
All snow is not created equal. Snow can have a wide range of moisture contents, and
this moisture content directly controls the weight the snow.
‘Dry’ snow, that light fluffy powdery stuff, is much lighter than the dense and heavy
‘wet’ snow. For example, two feet of a typical ‘dry’ snow will exert a load of
just under 10 lb/ft2 on a flat surface, while the same depth of a ‘wet’ snow can
exert over 40 lb/ft2.
Much of the snow we recently received was on the ‘wet’ end of the spectrum, and with
reports of over three feet of snow in some areas, maximum estimated ground snow
loads approached 70 lb/ft2. Even so, the actual snow load on a roof is often less
than the load on the ground. This is because winter winds can blow some of the
snow off of the building; however, if snow drifts occur on the roof, loads can
significantly increase. Typically, as roof slope increases, the snow load decreases
because snow tends to slide off instead of build up.
There are a number of reasons
why roofs can fail. If the actual snow load on the roof is greater than the design
load, then there is a danger of collapse. Improper building design and faulty construction
can also result in failure, as can older buildings that have been subjected to decay
or damage. 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
If you believe there is too much snow on your building, the best thing to do is
to remove it. Shovels, snow rakes, and brooms work well for this. This can be a
potentially dangerous task and should only be performed using the utmost caution
and safety procedures. There is often ice under the snow, and heed should be given
to any overhead electrical lines. For larger buildings, properly trained individuals
should be consulted as removing the snow in an unbalanced manner can result in
unequal point loads.
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.
Every fall, and before big storms, it is also a good idea make sure all gutters and
downspouts can flow freely to help prevent ice buildup and properly drain melting
snow off of roofs.