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As snowstorm Evelyn left a clear message — spring has not sprung — and dumped historic amounts of snow on much of the state this past weekend, several counties reported farm building damage and roof collapse on barns due to the snow. 

Additionally, there are many concerns for buildings that still have significant amounts of snow on them, especially if more snow falls before the current snow melts or slides off. 

“Snow and ice accumulations on roofs cause a loading which can cause roof collapse when the roof is not strong enough to resist the load,” said Brian Holmes, University of Wisconsin-Extension emeritus agricultural engineer.

Holmes added, “The more dense the snow and ice, the greater the load for a given depth. Wind blown-off and snow slide-off can reduce snow load on a roof. However snow drifting into leeward or lower roofs and valleys and snow slide onto lower roofs can add significant loads from accumulated snow.”

Aerica Bjurstrom, Kewaunee County UW-Extension agriculture agent, said there were about six to 10 farms in the county that had serious damage and a couple with livestock loss. 

"For the most part, everybody got their animals out safely," said Bjurstrom. 

With a few exceptions, the majority of the buildings that have failed are older freestalls, Bjurstrom noted. She's seen "a lot of failure in the ridge vents," which is more common in 90s style barn design. The center part of the roofs are falling through and the support beams are still holding up. 

Sleet turning into ice dumped around one-quarter to one-half inch of ice on roofs before the snow started, Bjurstrom estimated, adding to the weight on the roofs. 

Snow loading

In addition to estimating the roof loading, it’s important to know the loading the roof can resist, according to UW-Extension.

Wisconsin’s Uniform Dwelling Code requires most homes to have a minimum snow load rating of 30-40 pounds per square foot (lbs/ft2 ), with the greater requirement for Northern Wisconsin. Agricultural structures are exempt from this requirement.

Furthermore, structural failures can occur at snow loads less than the building was designed for if:

  • Structure was not designed, just built.
  • Trusses/rafters/purlins/ with reduced quality materials or smaller dimensions than specified in design were used.
  • Trusses/rafters/purlins installed at a wider spacing than specified.
  • Critical bracing not installed or improperly installed
  • Moisture condensed on or leaked onto structural members can cause decay/corrosion weakening the structure. Top chords of trusses, rafters, purlins and truss plates are particularly susceptible.
  • Loads added to the roof which were not considered in the original design. Examples include: ceiling, roof surface overlay, equipment installed on roof or hung from trusses.

The UW-Extension Service says that a ballpark estimate of snow load can be made with the following formula:

Calculated Roof Loading (lb/ft2) = Depth (ft) x Density (lb/ft2 /ft depth).

The approximate density (lb/ft2 /ft depth) for light snow is 5-20, packed snow 20-40, packed snow with ice 40-58, and ice 58. So for example, a roof with three feet of light snow has a estimated roof loading of 60 lb/ft2 (3 ft depth X 20 lb/ft2/ft depth density = 60 lb/ft2).

However, structural failure can happen even if snow loads are less than the building was designed to handle. UW-Extension provides these points to consider. 

  • Structure was not designed, just built.
  • Trusses/rafters/purlins/ with reduced quality materials or smaller dimensions than specified in design were used.
  • Trusses/rafters/purlins installed at a wider spacing than specified.
  • Critical bracing not installed or improperly installed
  • Moisture condensed on or leaked onto structural members can cause decay/corrosion weakening the structure. Top chords of trusses, rafters, purlins and truss plates are particularly susceptible.
  • Loads added to the roof which were not considered in the original design. Examples include: ceiling, roof surface overlay, equipment installed on roof or hung from trusses.

Removing snow

Bjurstrom said farmers should assess the situation before trying to remove snow or animals, watching for buckling and sagging of roofs.  

"A lot of people try to remove the snow off the roofs," said Bjurstrom. "Certainlly look very closely to make sure that it's going to hold people. Once you get up there and start disturbing it, you don't know what's going to happen. 

Bjurstrom has seen farmers use "interesting, creative ways" to get the snow off the roofs, using large blowers to blow salt onto the roofs, in one instance a crop duster flew over farm buildings dropping salt on the barns. Some go the route of asking fire departments for help spraying snow off the roofs.

"A lot are just going the old-fashioned way, getting a bunch of guys up on the roof and start shoveling," Bjurstrom said. "Roofs are slippery. That's adding additional danger to it, that's for sure."

Bjurstrom advises using caution when removing snow. Falls from roofs or from ladders going to the roof can easily occur. Removing snow can allow the snow up slope to suddenly slide down, burying people or animals below. Using a roof rake from a safe distance away can reduce some of this risk to the person removing the snow.

The UW-Extension offers precautions to follow when removing snow from a roof.

  • In uninsulated sheds, use a portable heater to warm the interior enough to encourage snow to slide off the roof so you don’t have to manually remove it. Unvented heaters can cause oxygen depletion and carbon monoxide accumulation in an unventilated space. Plan to ventilate the warmed shed before reentering.
  • Use a snow roof rake if at all possible. This allows you to stand on the ground in a safe place. Check the local hardware store or building supply store. Removing snow from the edge of the roof could allow snow above the edge to avalanche. Make sure you are out of the fall zone when scraping snow from a smooth roof surface.
  • Use fall protection equipment when workers are on the roof. Tie workers off so they don’t fall from the roof.
  • If ladders are used, locate and secure them so they do not fall while workers are standing on them. Also, locate ladders so they do not fall if snow slides off the roof knocking workers off the ladder or leaving them stranded on the roof.
  • Generally remove snow from the most heavily loaded areas first.
  • Remove snow in narrow strips instead of large areas to help keep loading somewhat uniform.
  • Don’t pile removed snow onto snow-covered roof areas increasing the load in those areas.
  • Use plastic shovels or wooden roof rakes to avoid damaging roofing material.
  • Don’t feel as if all snow must be removed. A layer of snow next to the roof surface can protect the surface from damage during the snow removal process.
  • Do not pick or chip at ice near the roof surface to avoid damaging roofing material.
  • Do not use snow blowers as they can damage the roof.

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 "We are certainly not out of the woods yet, because there's still a lot of snow on the roofs and we don't have a lot of sun," said Bjurstrom. 

Aside from the damage caused by roof collapse, Bjurstrom pointed out the potential for other long-term consequences, such as long-term injuries to animals and milk loss due to cows in less than ideal situations. 

The Dairy Business Association (DBA) is helping farmers that need to relocate cows due to a roof collapse, according to the DBA website and Facebook page

Farmers in need of a home for cows or who can accommodate another farmer's animals can contact Tim Trotter at (920) 643-6347 or ttrotter@widba.com, Nicole Barlass at (920) 980-3141 ornbarlass@widba.com, or Lauren Brey at (920) 392-1220 or lbrey@voiceofmilk.com.

"Although the snow has stopped falling, the risk increases as the snow melts and gets heavier. It is important to be alert and assess your buildings for damage regularly," DBA advises. 

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