As a rule of thumb, snow weighs approximately **20 pounds per cubic foot**, or 1.25 pounds per inch of depth. Depending on moisture content, snow can weigh from 1 pound per cubic foot to over 21 pounds per cubic foot.

Not only that, but moisture evaporates from snow over time, making it lighter and lighter as time goes on. And finally, 35 pounds per square foot is a minimum requirement. If you have ice dams, however, removing the snow is the good thing to do. Use a roof rake or hire someone to do it professionally.

The weight of one foot of fresh snow ranges from 3 pounds per square foot (psf) for light, dry snow to 21 psf for wet, heavy snow. When evaluating an existing roof for snow loads, an engineer will want to know the year it was built, the materials involved and the load the roof was designed to support, to start.

The maximum snow load of your roof depends on several factors, but the average roof can support about 20 pounds of snow per square inch. However, some areas of the U.S. that are prone to lots of snow may have roofs that support a heavier snow load. If the roof holds more weight than this, it can cause damage.

Calculated Roof Loading (lb/ft2) = Depth (ft) x Density (lb/ft2 /ft depth). The approximate density (lb/ft2 /ft depth) is: 5-20 for light snow. 20-40 for packed snow.

This downward imposed load on the home is also known as the snow load. The North Zone design live load equates to 40 pounds per square foot, the Middle Zone equates to 30 pounds per square foot, and the South Zone equates to 20 pounds per square foot.

House roofs should support 20 lbs./square foot of snow before they become stressed. Local building codes dictate the snow load required for residential roofs. Contact your local building code department to determine the snow load requirements for your area.

To figure out the load on your roof, take the depth of snow in feet and multiply it by the weight of a cubic foot of snow. If the snow weighs 10 pounds per cubic foot and there are 1.5 feet on the roof, each square foot of the roof is getting 15 pounds of pressure.

To calculate the weight of snow, you take 7.48 gallons of per cubic foot of water, which is about 62.4 pounds. You then divide it by the amount of snow (in inches). Light and fluffy snow weigh the least. If it snows 12” of light and fluffy snow, it will weigh about 5.2 pounds.

Roof loads are measured by pounds per square foot. The dead load of asphalt shingle roofs with wooden frames is usually 15 pounds per square foot (psf). Heavier residential roofing materials such as clay and slate have dead loads that reach up to 27 psf.

Live loads are those loads produced by the use and occupancy of a building or structure and do not include construction loads, environmental loads (such as wind loads, snow loads, rain loads, earthquake loads and flood loads) or dead loads (see the definition of “Live Load” in IBC 202).

Light fluffy snow may only weigh about seven pounds per cubic foot. More average snow may weigh 15 pounds per cubic foot and drifted compacted snow may weigh 20 pounds or more..."

A fluffy or dry snow weighs about 4 pounds per square foot. "Normal" snow comes in at 6 pounds per square foot. And a wet snow, is close to 13 pounds per square foot. Most houses can withstand 20 pounds per square foot.

According to the NWS, a standard snow shovel is about 1.5 square feet, so every shovel full of yesterday's snow weighs about 5.7 pounds. If your driveway is 18 feet by 20 feet and you shovel it clean this AM, you will have moved over a ton of snow!

In general, roof snow loads are somewhere between 50-90% of the ground snow load, depending on the exposure and heat transfer.

As a rule of thumb, snow weighs approximately 20 pounds per cubic foot, or 1.25 pounds per inch of depth. Depending on moisture content, snow can weigh from 1 pound per cubic foot to over 21 pounds per cubic foot. NOTE: Any ice build-up on the roof would need to be added to this formula.

A rule of thumb regarding the weight of light, fluffy snow: One inch of snow weighs 0.26 pounds per square foot. That means for every 6.5 inches of snowfall you've got the weight of a compact SUV on your roof. A rule of thumb regarding the weight of heavy, wet snow: One inch of snow weighs 1.66 pounds per square foot.

Last Revised: 11/04/2014. Once you have the ground snow load, p_{g}, you can compute the flat roof snow load, p_{f}. The design snow load represents the peak snow accumulation on a roof over the a winter season. In colder regions the design snow load represents snow deposited by multiple snow events.

At these slopes, snow creeps rather than slides and is easy to manage. On roof slopes between 4/12 and 6/12, rough textured roofing materials work best. They hold the snow in place and keep it from accumulating and then sliding off in large slabs that can be dangerous.

The weight of snow and ice

As weightless as snowflakes seem, combined into a layer of snow, they are heavy and can cause your roof to fail. The damage ranges from leaks to broken shingles and even roof collapse.

Roof pitches of 3:12, 4:12, 5:12, or 6:12 work best for metal buildings in snow country. Anything over a 6:12 pitch tends to make massive amounts of snow slide off the roof without warning. Anything less than 1:12 pitch is a huge mistake in snow-prone climates.

Most roofs can withstand 20 pounds per square foot of snow. However, there are many factors to consider when properly calculating your building's snow load. To calculate snow load, multiply the depth of snow in feet by the weight of a cubic foot of snow.

The dead load of a typical asphalt-shingled, wood-framed roof is about 15 pounds per square foot. The load increases with the use of heavier roofing material. A clay-tiled roof may have a dead load of as much as 27 psf.

Dead loads are loads that account for the weight of the roof structure itself. While the total design load may be 2 to 4 times greater than the design snow load alone, the weight of the snow, if it exceeds the design snow load, may cause structural failure.