How Much Snow Can a Roof Hold? Snow Load Explained for Metal Buildings

After the first heavy storm of the season, the question shows up in every Midwest group chat: how much snow can a roof hold before you need to worry? The honest answer is that it depends on what the roof was designed for and on what kind of snow is sitting on it. Depth alone tells you very little. This guide explains how snow load works, what snow actually weighs, how the rules differ for homes, garages and farm buildings in Wisconsin, and how to tell when a roof needs attention.

Snow load is measured in pounds, not inches

Engineers do not design a roof for a certain depth of snow. They design it for a snow load: the weight of snow the roof must carry, expressed in pounds per square foot (psf). Two numbers matter:

• Ground snow load. The weight of snow expected on the ground at a location, based on long-term weather records. It is the starting point for design and it varies from county to county.
• Roof snow load. The load the roof itself is designed to carry. It is calculated from the ground snow load and adjusted for things like roof slope, how exposed the building is to wind, and whether the building is heated.

That is why two buildings a mile apart can have the same snow on them and very different safety margins. The rating on the engineered drawings is what counts, not the depth on the lawn.

What does snow actually weigh?

Fresh powder and late-winter crust are not the same material. University of Wisconsin Extension guidance on snow loads for farm buildings gives these approximate weights for each foot of depth:

• Light snow: about 5 to 20 pounds per square foot per foot of depth
• Packed snow: about 20 to 40 pounds per square foot per foot of depth
• Packed snow with ice: about 40 to 58 pounds per square foot per foot of depth
• Ice: about 58 pounds per square foot per foot of depth

Emergency management agencies use a simpler rule of thumb. The Maine Emergency Management Agency's roof snow removal guidance estimates that 10 to 12 inches of new snow, 3 to 5 inches of old packed snow, or 1 inch of ice each weigh roughly 5 pounds per square foot. The takeaway is the same either way: a foot of wet, settled snow can weigh several times more than a foot of fresh powder, and rain falling on an existing snowpack adds weight quickly.

What Wisconsin requires — and where it stops

Rules depend on the type of building, which is where a lot of confusion starts.

• Homes. Wisconsin's Uniform Dwelling Code requires roofs on one- and two-family dwellings to support the minimum snow loads shown on the state's zone map for roof loads. UW Extension summarizes that as a minimum of 30 to 40 psf for most homes, with the higher figure in northern Wisconsin.
• Detached garages and accessory buildings. The state's own Uniform Dwelling Code overview lists detached garages and accessory buildings among the structures the UDC does not cover. Requirements for those come from your city, village, town or county, so they vary.
• Farm buildings. UW Extension notes that agricultural structures are exempt from the dwelling-code snow load requirement. Exempt does not mean immune: an under-designed machine shed carries the same snow as the house next to it.

Other Midwest states set their own rules, and local ordinances can be stricter than state minimums. Always confirm with the building department where the structure will stand.

How metal carports, garages and barns handle snow

A steel building does not get its strength from the thickness of the roof panels. It comes from the engineered frame underneath: the spacing of the bows or trusses, the gauge of the tubing, the bracing and the anchoring. Three things make the difference in snow country:

• Certification for the site. Every structure we install is engineer-certified for the snow load and wind at the location where it will stand. Your quote and drawings state the certified loads, so you are not guessing.
• A vertical roof. On a vertical roof the panels run from the ridge down to the eave, so snow and meltwater slide off instead of catching on horizontal ribs. We build vertical roofs as standard on buildings 32 feet wide and up, and recommend them for any carport or garage in a heavy-snow area.
• Frame options. Standard framing is 14-gauge steel tubing, with thicker 12-gauge tubing available as an upgrade.

We go deeper on roof style in our article on metal carports in Wisconsin's snowy winters, and you can compare structures on our metal carports, metal garages and steel barns pages.

Warning signs that a roof is overloaded

UW Extension and emergency management agencies list the same early signals. Take them seriously on any building, steel or wood:

• Sagging roof sections, or trusses and rafters that look bowed or out of line
• Creaking, cracking or popping sounds
• Doors that suddenly stick or pop open
• New cracks in walls, or bent or rippled supports

If you see or hear these, get people and animals out of the building first and have it inspected before anyone goes back in.

Removing snow safely

Most properly certified buildings never need to be cleared. When snow does need to come off, the published advice is consistent:

• Use a roof rake from the ground and stay well back from where the snow will land. Do not climb onto a snow-covered roof.
• Work in narrow strips and take load off evenly rather than clearing one side completely.
• Use plastic or wood tools, not metal edges, and leave a thin layer of snow so you do not scrape the roof surface.
• Do not chip at ice on the panels and do not pile removed snow onto another roof.

Frequently asked questions

How many inches of snow is 20 pounds per square foot?

It depends on the snow. Using the common rule of thumb of about 5 psf for every 10 to 12 inches of fresh snow or every 3 to 5 inches of old packed snow, 20 psf is roughly 3 to 4 feet of fresh snow but only about 1 to 2 feet of packed snow.

Is a steeper roof better for snow?

Generally, yes. Snow slides off a steeper, smoother roof more easily, which is one reason design loads account for slope. Panel direction matters too: vertical panels shed snow better than horizontal ones.

Do carports have a snow load rating?

Engineer-certified ones do. The certified snow and wind loads are stated on the drawings for the structure. If a carport has no certification, there is no documented rating to rely on.

How do I find the snow load for my address?

Ask your local building department, which enforces the requirement for your property. When you request a quote from us, we research the local requirement and certify the building to it.

Build for the snow you actually get

Send us your ZIP code and the size you have in mind and we will quote a steel carport, garage or barn certified for your local snow and wind loads. Request a free quote, design it yourself in 3D, or call (262) 383-4347.

This guide is general information. Snow and wind load requirements, certification details and permit rules must be confirmed for your property with a Wisconsin Carports Building Specialist and your municipality.

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