Constructing Pole Barns for Snow Loads

How to Make Sure Your Pole Barn is up to the Challenge

Mother Nature has become a headline grabber:

“Record-breaking winter weather grips Northern U.S.” – The New York Times, Dec. 27, 2017

“April looks to deliver another record-breaking snowstorm” – Minneapolis Star Tribune, April 10, 2019

And it’s not just hype. Consider these statistics:

• According to the MPR News “Updraft” blog, Eau Claire, Wisc., recorded more than 200% of its average snowfall during the 2018-19 winter season.
• WeatherNationTV.com reported that February 2019 was the fourth snowiest month of all time for Minneapolis-St. Paul; and Duluth accumulated nearly three times as much snow as normal for February, surpassing an 80-year-old record. The online weather site also stated that Omaha, Neb., had more snow during February 2019 than it averages during an entire year.

As fun as it might be to read stats like this, record breaking snowfalls can take an enormous toll on people — and agricultural buildings. This past winter, for example, one insurance company alone reported 250 collapsed roofs and buildings – mostly pole barns – throughout Minnesota and North Dakota.

“It was a combination of weather phenomena,” said Dean Kerfeld of RAM Mutual Insurance, which primarily underwrites agricultural buildings. “We had about two months of continuous snowfall without any intervening temperatures warm enough to melt and cause at least some snow to slide off metal roofs.”

What’s noteworthy, Kerfeld added, was that of the 250 claims RAM Mutual processed, not one of those buildings was what is considered “engineered” – meaning that the failed buildings were designed with little to no consideration for how much stress they might have to withstand. Heavy snow loads on roofs can cause an extreme amount of stress, so it’s important to make sure your buildings can carry the weight.

How heavy is snow? According to the Federal Emergency Management Agency’s snow load safety guide, “The weight of 1 foot of fresh snow ranges from 3 pounds per square foot for light, dry snow to 21 pounds per square foot for wet, heavy snow.” Add one inch of ice to the mix and your totals will increase “a little less than 5 pounds per square foot.”

What’s more, drifting will occur, and your building must be designed to handle higher loads in areas where snow will accumulate in larger quantities. “The height of a snow drift on the leeward side of the ridge depends on ridge construction and increases as building width increases. Such drifts can be several feet high in wide buildings,” said David Bohnhoff, Emeritus Professor at the University of Wisconsin, Madison, College of Agricultural and Life Sciences. “Snow will also accumulate in valleys formed by intersecting roofs, on sides of parapets, at abrupt changes in roof height, and generally anywhere else there is a change in roof geometry.”

“Building length can influence the size of snow drifts as well,” he said, “and in real long buildings, you need to guard against a progressive roof collapse – a collapse in which a small local failure brings down a large portion of the roof in a domino-like fashion.”

Unfortunately, the majority of ag buildings aren’t protected by construction codes the way residential and commercial structures are. Most codes in northern U.S. climates require the roofs on houses and commercial spaces to support 30-40 pounds per square foot but, “Ag buildings in many states are often code exempt because the activity that occurs in them is considered less of a risk than activity that occurs in a residential or commercial building,” explained Joe Bjelland, Territory Manager for Lester Buildings.

However, the risk to farmers and other ag building owners is still considerable, said Professor Bohnhoff. “If you own a milking parlor and that roof collapses, not only might you have to pay to deal with dead or injured animals, you also have the time, cost and inconvenience of relocating surviving cows and repairing or replacing the building. There is also the long-term drop in milk production that occurs with a disruption in normal lactation, and animal stress associated with relocation to a new environment. That’s money you’ll never get back.”

Even if your pole barn “just houses machinery,” you’ll want to make sure the roof can withstand the worst Mother Nature throws at it. “You could have a building that’s worth only $130,000, but it could be protecting $2 – $3 million in assets when you factor in how much combines, planters and other equipment costs,” Kerfeld said.

Engineered Buildings 101

Because ag buildings are largely code exempt, “you can build to whatever load you want,” said Paul Boor, Structural Engineer at Lester Buildings. “But, as we’ve seen, what goes on in those buildings is far more valuable than the structures themselves. It pays to spend a little more to protect that investment.”

Here are a few factors to consider if you’re planning a new pole barn construction project:

1. Know the difference between an engineered truss and an engineered building
Whether you get them from a lumber yard or a specialized building contractor, most trusses are considered engineered. However, using engineered trusses doesn’t mean you’re erecting an engineered building. “For example, if you have really strong trusses, but your purlins aren’t as strong, or you have headers that aren’t sized properly, you increase the chances that the building will fail prematurely,” Boor explained. “The secret to an engineered building is that there’s a guaranteed load path going from the roof all the way to the footings.”

2. Build a little stronger building that you think you’ll need
Weather patterns are changing, and we’re seeing more high snow events and maximum wind speeds (which can make drifting worse) than in days gone by, so snow loads can add up quickly and unexpectedly. “We routinely designed 20-pound ag buildings in the past in Minnesota,” Boor said. “But now we’re recommending 25-pounds. If I were an owner, I’d go even higher because it’s inexpensive to design for increased loads, but much more costly to try to change it after the building’s up.”

3. Check with your insurance
Before the excavator ever arrives onsite, check with your insurance company. Some carriers, like RAM Mutual, offer premium discounts to policy owners who construct engineered buildings.

4. Don’t be fooled by a lower price tag
It’s easy to understand the desire to save money when you’re building a new building, but if you see two pole barns that look exactly the same and one’s cheaper than the other, start asking questions. Find out the difference in each building’s design. More than likely, the one with a slightly higher price tag is engineered and will withstand the test of time and weather.

“Based on preliminary investigations, there’s little doubt that a large percentage of post frame buildings that failed this past winter weren’t structurally engineered,” said Professor Bohnhoff. “While you can’t always assume that there’s a single reason why a building fails, it’s always a good idea to build a structurally engineered building.”

5. Give us a call
Since 1947, Lester Building Systems has been constructing engineered pole barns that stand the test of time. Contact us to get started on your dream building.