Prevent roof collapses due to heavy snow

Posted at 3 p.m. on February 13, 2019

This story originally appeared in April of 2018 after a blizzard that caused a number of barn roofs to collapse. Circumstances have repeated themselves in the February 12 snowstorm, and so we are re-publishing this article as a public service.

By Ed Byrne

The Brillion News

The Great April Blizzard of 2018 was costly for many farmers in the area. The storm produced up to 33 inches of heavy, wet snow, and the thick layer of “frosting” turned out to be more than the roofs of many barns, industrial and commercial buildings could support.

Rural fire departments were dispatched at a half-dozen farms in the area to help prevent roof collapses, mostly on free-stall barns, the barns that dominate on large dairy farms in the area – the confined animal feeding operations (CAFOs).

Unlike the barns of old, the new free-stall barns are wide and have roofs without significant pitch. The roofs are supported by long trusses, and many were never designed to support the load created by two to three feet of heavy, wet snow – the kind of snow typical in the front and back ends of winter in the Upper Midwest.

A professor with the University of Minnesota-Extension, Kevin A. Janni, has written extensively about the danger of barn roof collapses.

“Winter storms in Minnesota and other sections of the upper Midwest can dump large amounts of snow and ice on agricultural building roofs which can lead to a roof collapse,” Janni wrote. “Building owners can do several things to reduce the chances of a roof collapse.”

When a barn roof begins to fail, it is a sign that it was not designed for the reality of winter in state like North Dakota, Minnesota, Wisconsin, Michigan, Vermont, New Hampshire or Maine.

In Minnesota, the roof snow load for residential buildings is set by state code and is 42 pounds per square foot (psf) in northern Minnesota and 35 psf in southern Minnesota.

Because barns do not house people, a lower standard is used for them.

“Many agricultural buildings are built using a 20 psf snow load which would be expected to handle four feet of dry snow or two feet of wet, heavy snow and ice,” Janni said.

He said that some people combine the snow load with the building dead load (i.e., weight of the roofing and trusses). When a farmer is talking with his building designer, he needs to make it clear that the total load is the target: the structure must be designed to support both the weight of the roofing and trusses, plus the weight of the worst snow you expect to see.

Janni said that numerous factors affect the amount of snow that can build up on a roof, including:

1. Roof pitch – Snow will not easily slide off flatter roofs (40 degree pitch or less).

2. Drifting – Wind blowing snow around can create drifts producing uneven or unbalanced snow loads of a roof.

3. Roof material – Shingled roof decks do not shed snow and ice as easily as metal roofs.

4. Roof valleys – Roof areas which collect a lot of snow produce significant load on those areas.

Metal structures often don’t give much warning before collapse, whereas structures with wooden posts, beams and trusses often do.

Here are some tell-tale warning signs cited by the The Bullvine dairy newsletter: Sagging roof; severe roof leak; doors popping open; sudden emergence of cracks in walls or masonry; bends or ripples in supports; visible bowing of rafters; cracks or splits in beams and posts; screws in steel frames shearing off; creaking, cracking or popping sounds; doors or windows that suddenly stick or won’t open; bowing or bending of utility pipes or conduit at the ceiling.

Preventing collapse

Getting the snow load off the roof as soon as possible is the best way to prevent a collapse. Start with the area with the area of the deepest/heaviest snow load.

In most cases, there is some time – but not a lot – between the end of the snow event and structural failure.

Before doing anything, the farm needs to assess the potential for a collapse, and get people and livestock out if there is a fear of structural failure.

The UMN Extension advocates an inspection to look for signs of structural damage or. Look at the sidewalls to see if there are any bulges or indications that knee braces have failed.

Look at the roof line from the outside to see if it is still straight.

Look at the ceiling, open trusses and walls from the inside for indications of damage or failure.

“If there are indications of building damage or failure, do not climb onto the roof or enter the building while the snow is on the roof,” Janni said.

A roof that is already under stress does not need the weight of a person added to the load.

One way to remove snow from a roof is to physically get up on the roof and shovel it off, but serious injuries are possible if a person falls from a snow-covered and icy roof.

The University of Wisconsin Extension recommends that anyone of the roof to shovel show wear a safety harness. If a person is on the roof when it collapses, he could be crushed or buried.

The shoveler should use ladders, safety ropes and take necessary precautions.

Other options include using snow rakes that can be used from the ground or from portable scaffolding. When using a snow rake or specialty tools use extreme caution when working near overhead electrical power lines.

Snow rakes can damage the roof if not used cautiously

If the weather is not too cold (i.e. 20 degrees F or higher), hot water or some other heat source can be used to melt snow and ice.

You can also warm the inside of the building with large heaters to melt the ice layer, and then waiting for the snow and ice to slide off. The building must be an open-trussed structure and have a non-insulated metal roof.

Make sure that no people, animals or equipment are in the area where the snow and ice fall as they slide down the roof.

One insurance company recommends raking snow down in narrow strips to keep the load somewhat even.

Next year

Many farmers who had structural damage to free-stall barns will have to make sure the buildings are safe for people and livestock.

That damage could make them vulnerable to collapse next winter, even under a lighter snow load. Assessing the damage, and planning to restore structural integrity should be priorities.

AIG Insurance recommends checking the structural integrity of every farm building a month before the expected start of winter.

AIG also notes that a barn can be designed for a particular snow load, but changes to the building can compromise that design integrity – such things as adding solar panels, new lighting, heaters, ceiling fans, a sprinkler system, roof insulation

The Nationwide Mutual Insurance Company recommends getting an accurate assessment of the barn’s roof load, and then rebuilding or fortifying them so they can withstand a worst-case scenario snow load in the future.

Nationwide also suggests checking with your insurance carrier to make sure your property insurance covers roof or building failure due to snow load, to make sure the policy covers actual replacement costs; and to make sure that insurance covers equipment in the barn that is destroyed or damaged in a collapse.

Lessons learned this winter in Northeast Wisconsin can be applied to plans for new free-stall barns.

Traditional barns were designed with roof pitches ranging between 30 and 55 degrees, and they seldom has any damage due to snow loading.

The majority of new free-stall barns and sheds have roofs pitched at around 15 degrees – and they are vulnerable to collapse under heavy snow loads.

Farmers today may need to consider the wisdom of roofs with a greater pitch when designing a new structure.

~ Sources: Cornell University, Penn State, University of Wisconsin Extension, University of Minnesota Extension, AIG Insurance, Nationwide Insurance.