GILMANTON, Wis. – Excessive snow and blowing wind create a nasty combination – a danger that caused a record number of farm buildings to collapse this past winter. Weather events can’t be controlled so farmers need to do what they can to prevent damage.
That starts with building design, says Aaron Halberg, resident professional engineer at Halberg Engineering.
“We should avoid all possible loss,” he said at a presentation sponsored by University of Wisconsin-Extension in Buffalo County
Carl Duley, UW-extension agent, said collapsed buildings aren’t a new issue but buildings are becoming bigger, which puts more stress on construction materials. This past winter collapsed buildings in west-central Wisconsin had more than $12 million in damage. That included poultry sheds, machine sheds, livestock barns and grain bins that ranged from one to 50 years old. Damaged buildings continued to drop throughout the spring.
Once snow piles up, wind can change the depth and density of snow on a roof. Rain on the snow can increase the weight by 5 pounds per square foot for every inch. Ice dams can form along the edge, holding snow back from sliding off the roof. Something as small as screw heads showing through a roof is enough to hold snow on a roof.
Wisconsin has no binding building code for post-frame buildings, although standards do exist. Halberg referred to ASCE 7, a minimum-design load, as a source for building design – with the caveat that codes are a minimum. A project may need greater design loads. Factors such as building use, the presence of animals or humans, and siting need to be considered
Halberg recommends dealing with people who have been in the business for a while – those with a good design reputation and warranty on the work. He warns that the cheapest building might be just that – cheap.
“When I see a collapse, it’s usually one or two details that were missed,” he said.
Duley gave an example.
”Steel isn’t steel isn’t steel,” he said.
If a builder downgrades the steel, connectors can rust. That results in less building integrity.
Design should start with load considerations, Halberg said, and then trusses, trusses to posts, overall connection and bracing. Every link in the chain is important. Designers should consider what happens when doors are open or closed as well as extra dead weight such as solar panels or insulation.
Once building construction starts it’s expensive to make changes in the load rating and can be complicated. In existing structures it may be possible to fix a weak spot by reinforcing purlins, adding material to trusses or bolstering connections.
For older sheds, lean-tos are a popular way to cheaply add more building. But they can put stress on the original building. Also they catch snow; they need to be properly attached.
If a structure fails it’s important to have insurance to cover losses. Several issues will determine whether insurance will pay for damage and how much they pay, Duley said.
- insurance for snow load
- building that’s covered but not equipment or animals
- falling objects
- buildings too old for insurance
- replacement cost vs. depreciated value
He said farmers should consider coverage for loss of production.
Insurance companies use three categories for coverage.
- Actual Cash Value
- Replacement Cost Value
- Functional Replacement Value
The actual cause of damage will be considered – whether for example it was snow load or snow load with wind. If the snow was there previous to the wind damage will be considered.
“We don’t ask enough questions,” Duley said of insurance agents. “The biggest message I have about insurance is to read your policy and know what’s in it. Have a conversation with your agent.
“Not all policies are the same; don’t assume anything.”
Halberg and Duley both said owners deserve enough information to decide what’s best for their buildings.
“We need to be moving in a smarter direction in building design.” Halberg said.