Prevent roof collapses from snow and ice
- 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.
- The amount of snow or ice that is unsafe depends on the building design.
- In most cases, agricultural buildings will have an excessive snow load if there are more than four to six feet of snow on the roof.
- Building owners can do several things to reduce the chances of a roof collapse.
Build a structure to withstand snow loads
One preventive measure is to build a structure that is properly designed and constructed to meet or exceed expected snow loads from winter storms.
- Buildings can be designed based on the amount of snow expected from storms once in 25, 50 or more years.
- The roof snow load for residential buildings in Minnesota is set by state statutes and is 42 pounds per square foot (psf) in northern Minnesota and 35 psf in southern Minnesota.
Agricultural buildings can be built with lower snow load design values because the building importance for agricultural buildings can be set lower than for residential buildings. 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.
Some people combine the snow load with the building dead load (i.e., weight of the roofing and trusses). Be clear when talking with your building designer.
Plant snow fences or tree shelterbelts
Effective snow fences or tree shelterbelts upwind of farmsteads and agricultural buildings can help you avoid excessive snow on building roofs.
Proper snow fence design and location is important for protecting a building or farmstead. Some building roofs have failed in the past because the buildings were located too close to shelterbelts or windbreaks, which resulted in large snow drifts on top of these buildings.
Remember that, when placing a 50 percent solid snow fence or tree windbreak, snow will be deposited downwind a distance of up to 10 times the shelter belt or snow fence height.
- An 85 percent solid fence deposits the snow within a distance of about four times the fence height.
- Porous snow fences distribute the snow more evenly and give better protection downwind than a solid fence.
Leaving an area for snow to accumulate is very important when locating a machine shed or livestock building downwind from a shelterbelt. If the building is too close, it will be within this snow drop area. If too far from the windbreak, it will be outside of the wind “protection” zone. Learn more about windbreaks and living snow fences.
What could increase snow build up on a roof?
- Roof pitch: snow will not easily slide off flatter roofs (3/12 pitch or less)
- Drifting: wind blowing snow around other buildings, trees and roof structures (ex. cupolas) can create huge snow drifts and uneven or unbalanced snow loads of a roof
- Roofs on other lower buildings or “lean tos” that “receive” snow or ice sliding off another roof above it
- Shingled or roof decks do not shed snow and ice as easily as metal roofs
- Roof valleys or roof areas that collect a lot of snow
What can you do if your building has deep snow on it?
Get the deepest snow off as soon as possible
Generally, you will have some time between a large snowfall event and possible structural failure.
Check for danger signs
Before beginning to remove snow or enter a building with excessive snow on the roof, look for signs of building damage and the beginning of failure.
- Look at the sidewalls to see if there are any bulges or indications that knee braces have failed.
- Look at the roof line to see if it is still straight.
- When entering a building with excessive snow, look at the ceiling, open trusses and walls 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.
Snow removal methods
- Hire a professional if possible.
- Get up on the roof and shovel off the snow. There is a danger of falling off the roof when working on a snow-covered and icy roof. Use ladders, safety ropes and take necessary precautions.
- Use snow rakes or specialty tools that can be used from the ground or from portable scaffolding.
- Use extreme caution when working near overhead electrical power lines.
- Avoid excessive scraping on the roof or trying to chip off the ice. These practices can damage the roof and lead to a leaky roof.
- If the weather is not too cold, hot water or some other heat source can be used to melt snow and ice.
- Warm the inside of the building sufficiently with large heaters to melt the ice layer and then wait for the snow and ice to slide off.
- A lot of heat is necessary for even a moderately-sized building, and the building must be an open-trussed structure (no flat ceiling) and have an uninsulated metal roof.
- Be careful to prevent large chunks of ice and snow that slide off the roof from falling on people, animals or equipment.
- Do not put heaters in an attic of buildings with flat ceilings because of the fire and carbon monoxide danger and you could create ice dams along the building's eaves.
It is difficult to say how much snow or ice is safe because it depends on the building design and the snow or ice weight. In most cases, agricultural buildings will have an excessive snow load if there are more than four to six feet of snow on the roof.
Excessive snow and ice followed with cold temperatures can create excessive snow loads. You should monitor the snow load situation on your agricultural buildings and take appropriate action. Check high risks areas and, if you need to remove snow, please be extremely careful.
Reviewed in 2016