Farm buildings and snow load
By Tina LeBrun
and Wayne Schoper
South Central College
This winter has seen the drought continue that has plagued us since last May. While a lack of snow does mean safer travel and lower snow removal budgets, the moisture that we receive during the winter months adds up to supply growing season water for crop production. As the winter goes on, we will probably receive more snow and as it melts and refreezes into ice, we can expect more stories of roof problems and damage. If we do get a sudden influx of snow, we need to monitor the snow load situation on all of our farm buildings. Some will slide off once we get a few days with melting temperature. But if the melting snow refreezes before it can run off the roof we can end up with a bigger problem in the form of ice dams and water damage.
Be sure to check high-risk areas, and if you need to remove snow be extremely careful. Snow and ice storms can leave several inches and/or feet of snow on some roofs, which can add 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 does during the winter months. If the ice layer does not melt, each additional snowfall during the year will intensify the problem.
Snow loads for agricultural buildings in much of southern Minnesota are generally around 20 pounds per square foot. This level of loading is not intended to last all winter. Thus over the course of time a fatigue factor sets in and moderate to severe damage can occur. A roof may be able to support the designed snow load for several days or a few weeks, but probably no more than 30 days.
So what should 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 structure 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 broom or shovel it off. There obviously is the safety concern of falling off the roof when working on a snow-covered and icy roof. It’s important to use ladders, safety ropes and to 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 leaking roof.
There are other more innovative methods of removing snow and ice from roofs. One involves warming the inside of the building sufficiently with artificial heat to melt the snow and ice. Obviously a lot of heat is necessary for even a moderately-sized building and it must be an open-trussed structure (no flat ceiling). It also must not be insulated for obvious reasons. Caution is necessary to prevent large chunks of ice and snow that fall off of the roof from falling on people, animals or equipment. For flat-ceiling buildings, putting heaters in the attic is generally not recommended. The fire danger is too high and severe ice dams may be formed along the eaves of the building.
The message here is, if we do receive a lot of snow yet this winter, to take the time to look at the snow load on all of your farm buildings. Some of the older structures are especially at risk and need to be treated with extreme care. Consider moving livestock out of any building that appears to be under extreme stress. And take care to avoid putting yourself or others in danger.