Look at roof design, snow load when assessing collapse
risk
By Larry D. Jacobson and Kevin A. Janni, University
of Minnesota Extension
After the many recent
roof collapses of agricultural buildings caused by excessive
snow loads, we have been monitoring conditions in a
research effort to relieve or reduce the amount of snow
that builds up on a roof. Although people are rightfully
concerned about their other buildings once they’ve
had one collapse, buildings handle snow loads differently.
The collapse of one building doesn’t necessarily
mean all the buildings on the farm are in danger.
More information will be available when our data gathering
and analysis is complete. Currently, indications are
that the following factors affect the amount of snow
that can build up on a roof:
roof pitch (snow will not easily slide off flatter roofs
of 3/12 slope or less)
drifting (wind blowing snow around other buildings and
trees can create huge snow drifts and uneven snow loads)
“lean-to” roofs or roofs on other lower
buildings that “receive” snow or ice sliding
off another roof above it
shingled or roof decks which do not shed snow as easily
as metal roofs
roof valleys or areas which collect a lot of snow
As a general rule of thumb, remove snow if there are
more than four feet of dry snow, or more than two feet
of heavy, wet snow and ice on the roof. For information
on removing excessive snow loads, and important safety
recommendations, see our column “Watch farm buildings
for excessive snow loads; remove with extreme caution”
on the University of Minnesota Extension website at
www.extension.umn.edu/news. Look for the Dec. 29 column
in the short list.
A preventive measure to avoid excessive snow on building
roofs in future years is to have effective snow fences
and or a tree (shelterbelt) windbreak for farmsteads
and/or agricultural buildings. Some of the buildings
that have failed this year were located either too close
to shelterbelts and/or windbreaks or there was no protection
for the buildings at all, resulting in large snow drifts
on top of these buildings.
For more information on shelter belts and snow fences,
see University of Minnesota Extension’s online
publication “Living Snow Fences.” Go to
the Extension website at www.extension.umn.edu and enter
“living snow fences” in the search bar.
For more detail on snow fences in relation to agricultural
buildings, see North Dakota State University’s
online publication "Farmstead Windbreak Design"
at www.ag.ndsu.edu and enter “farmstead windbreak
design” in the search bar.
If we continue to receive average or above normal snowfalls,
monitor the snow load situation on agricultural buildings
and take appropriate action. Check high risks areas,
and if you need to remove snow please be extremely careful.
