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This story was originally published on Dec. 5, 2023.
Kami Rivera kept a close eye on her 250-year-old barn as Monday’s storm piled several inches of snow on its roof. She did not have to shovel it off this time, but she knows never to take snow loads for granted on any of her buildings — especially the ones housing animals.
Snow load refers to the downward force on a building’s roof created by the weight of snow and ice. When that load gets too heavy for the building to withstand, the roof or entire structure can collapse under tons of snow.
An imbalance of drifting snow piling up in one corner of a roof can cause one part of the roof to give way, resulting in a domino effect that could collapse the entire structure.
Most people in Maine know they should pay attention to the amount of snow piling up on their residential roofs and decks during winter. When too much snow builds up, there is a higher risk for leaks and structural damage. The risk is no less for barns and outbuildings, especially some of the older, less sturdy ones that dot the state’s landscape.
Earlier this year five cows were killed and dozens of other animals injured when a barn collapsed in Union. Snow buildup from a series of storms was blamed for creating too much structural stress.
That’s why Rivera eyeballs her Frankfort barn that houses eight horses each snowstorm to make sure it is not under too much snow load.
Factors that can play into how much snow collects include how protected the roof is from the wind, if the building is heated, the slope of the roof and the roofing material.
Newer buildings, including barns and other homestead outbuildings, can be built taking into account the average snow load in a winter. That information is available through the state, which maintains a list of 684 communities and their average annual snow loads.
Bangor, for example, has an annual winter snow load average of 90 pounds per square foot.
Unless your building is rated for that heavy amount of snow, you need to remove snow before it gets to that point.
Don’t think quonset-type buildings are safe simply because the snow builds up along the sides, not on their curved roofs. Too much snow can create enough pressure to crumple the sides inward.
All it takes to estimate how much snow is on your roof is a bit of basic math and knowledge of different types of snow.
Generally speaking, structural engineers assume light snow weighs up to 20 pounds per square foot. Packed snow weighs between 20 and 40 pounds per square foot.
Packed snow with ice can weigh from 40 to 58 pounds per square foot, and pure ice comes in at 58 pounds per square foot.
Once you determine what kind of snow you have, it’s time to measure the depth on the roof. Then multiply the depth in feet by the pounds per square foot.
A roof with three feet of light snow covering it would be under a load of 60 pounds per square foot.
Based on that and your own experience with your roofs, you can decide whether it’s time to remove snow.
Because barns and outbuildings are often some distance away from the residence or out in a field, it’s a good idea to have a solid plan in place before the first snowflake of the season falls. You don’t want your buildings to become victims of an out-of-sight, out-of-mind approach.
Insurance companies recommend having a plan for each building based on its specific snow load design or on your estimate of what it can hold.
The plans should include who is responsible for checking the roofs, how often they are checked, who’s responsible for snow removal — either personally or for hiring someone to do it — and how deep the snow has to be on the roof before it must be removed.
It’s also important to inspect buildings in the warmer months in case roof repairs are needed.
Heading into winter, Rivera is confident that she and her barn, built in 1774, are ready, especially since most of the snow load takes care of itself.
“The pitch of the roof and the metal roofing allow the snow to slide off,” she said. “I’ve only had to shovel snow off the little shed on the side.”
She recommends other homesteaders take the time to check out their buildings and, even if it’s only a precaution, shovel any spots where the snow is piling up.
