Reduce risk of collapse by clearing roofs of snow

Larry Jacobson

Published 12:00 p.m., March 3, 2007

Recent weather conditions in Minnesota may result in excessive roof loads on agricultural buildings due to the accumulation of snow and ice.

The month of March will hopefully provide some opportunity for the existing ice and snow on roofs to melt or slide off.

However, if we continue to receive above normal snowfalls, you should monitor the snow load situation on your agricultural buildings and take appropriate action.

Check high-risks areas, and if you need to remove snow, be extremely careful.

Snow and ice storms that have hit the state have left several inches of ice and/or several feet of snow on some roofs, which have added to the total weight that trusses and rafters must support.

Because of this ice layer, snow that has recently fallen on a typical metal roof is not sliding off like it normally does in the winter. If the ice layer doesn't melt, each additional snowfall this year will intensify the problem.

Snow loads for agricultural buildings in much of southern and western Minnesota are generally around 20 pounds per square foot.

This level of loading is not intended to last all winter; there is a fatigue factor. A roof may be able to support the designed snow load for several days or a few weeks, probably no more than 30 days.

So what do you do if you have too much snow on your roof?

The simple answer is to get it off as soon as possible. Generally there is some time between a large snowfall event and possible structural failure.

Unfortunately, one good way to remove snow from a roof is to physically get up on the roof and push the snow off with a shovel and/or broom.

There obviously is the safety concern of falling off when working on a snow-covered and icy roof. It's important to use ladders, safety ropes and take necessary precautions. Snow rakes also can be used to remove snow.

When using a snow rake, use extreme caution when working near overhead electrical power lines. Also, avoid excessive scraping on the roof or trying to chip off ice. These practices can damage the roof and lead to a leaky roof.

There are other, more "innovative" methods of removing snow and ice from roofs. One involves warming the inside of the building sufficiently with large heaters to melt the ice layer, and then hoping the snow and ice slide off.

Obviously, a lot of heat is necessary for even a moderately-sized building, and it must be an open-trussed structure (no flat ceiling), and have an uninsulated metal roof.

Caution is necessary to prevent large chunks of ice and snow that slide off the roof from falling on people, animals or equipment.

For flat ceiling buildings, putting heaters in the attic is generally not recommended. That's because of the fire danger and the possibility of creating ice dams along the building's eaves.

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Larry Jacobson is a professor and agricultural engineer with the University of Minnesota Extension.