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How to design a freestall barn for snow loads

Auz Burger for Progressive Dairy Published on 11 December 2021
Freestall barn

While a blanket of snow covering the landscape may be a beautiful sight for some, it can also be a warning sign on some dairies if a building’s roof is not designed to handle heavy snowfall.

The risk of a roof collapsing and causing harm to cattle or people is one a dairy owner does not want to take. That’s why it is crucial to any dairy farm to use a barn design that will be able to stand up to a heavy snow load.

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A steel freestall barn can be designed to handle a heavy snow load, keeping your cattle safe and your roof where it belongs.

Why steel for a freestall barn?

One of the strongest building materials available is steel, making it a good option for handling a heavy snow load. The average snow load in your area is also factored into the design of the freestall barn to ensure your building will be able to handle the winter on your dairy farm.

What is a snow load?

One cubic foot of snow equals one snow load, and it usually weighs between 10 and 15 pounds; if it is compacted, it can weigh up to 20 pounds. This is how engineers estimate the support your roof will need in order to withstand the snow load in your region.

If your dairy farm is in an area that receives a heavy snow load each year, like Wisconsin or Minnesota, your barn roof will need to be able to support at least 60 snow loads – but often higher.

Risks of snow on your freestall barn roof

If your roof is not sturdy enough for the snow load in your area, you face the risk of the roof collapsing, especially if it builds up quickly and is not cleared off. You also run the risk of ice dams, which is when the snow starts to melt and the runoff flows into the gutters before freezing. These can eventually lead to leaks, and the gutters and shingles on the roof can begin to fall.

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Designing a freestall barn for snow loads

When designing your freestall barn, there are a few things to consider to help your barn withstand your snow loads.

Roof pitch is key for snow

One of the best ways for a steel freestall barn to handle snow is by using a 1:12 roof pitch instead of a 6:12 pitch, which can be specifically engineered to bear the weight of snow in your area. The higher roof pitch will help your freestall barn clear snow as it falls and gives it somewhere to go when it begins melting. This will prevent melting snow from turning into little puddles on the roof, which can lead to additional problems. You will want to consider drainage too, to ensure you are giving the melted snow a way to get off your roof quickly.

If your roof pitch is not designed for the snow load in your area, it might build up and suddenly slide down when it becomes too heavy – this is called a roof avalanche. These are unpredictable, and they can harm your roof and gutters as well as any people or animals who happen to be under them at the time it happens; it can even hurt any landscaping under the roof. Keep in mind the potential for uneven snow distribution when you design your roof pitch; this is an important part of keeping your freestall barn roof safe.

Using purlins and trusses

The purlin is a horizontal beam that sits on the main rafter of the roof. Spacing purlins close together in parts of your freestall barn roof that may build up more snow can help the roof support a heavier snow load.

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Trusses are also spaced close together to help a roof support snow loads. The spacing of the trusses will depend on the snow load in your region.

Ventilation and snow loads

Since cows produce large amounts of heat and moisture on their own, ventilation is one of the most essential things to consider when designing a freestall barn. Even during a cold and snowy night, cows need to get fresh air from outside coming in to keep them healthy and reduce the heat and humidity inside the barn.

One of the most common ways to add ventilation in the winter is by having a ridge in the roofing that allows the humid air to escape and let in the cool, dry air. If your roof pitch is calculated well, you will not have to worry about the ridge letting in snow or melting snow getting inside. If need be, you can always add a gutter along the ventilation ridge to help guide the snow and water off of the roof and away from the ridge. end mark

PHOTO: This barn has a low roof pitch to help the snow slide off of it, and it has multiple gutters and drains to direct the snow when it begins to melt. Photo courtesy of General Steel.

Auz Burger is an expert in steel buildings and a writer for General Steel. Email Auz Burger

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