Snow Depth On A Roof

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.

Snow depth on a roof.

Snow design loads are based on figures published by the asce. Overestimation of snow loads can unnecessarily increase the cost of construction. They hold the snow in place and keep it from accumulating and then sliding off in large slabs that can be dangerous. These questions aren t quite so easy to answer because there are several variables.

How much snow a roof can hold depends on the type of snow roofline and material among other considerations. On roof slopes between 4 12 and 6 12 rough textured roofing materials work best. Estimates for the actual weight of snow range from 1 to 1 5 psf per inch of depth. 2 2 3 regional and local considerations.

In a 6 inch snowfall an inch of snow has a design density of 1 25 psf per inch and a real world density closer to 1 psf per inch. 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. Intuitively this is the number of inches of snow on your roof in the place where the cover is the thickest. Fresh fallen snow is often very lose compacted to snow even an hour old.

In the high snow areas an additional problem occurs in that after several snow falls with periods of partial melting and or heat loss through the roof the layer against the roof may. Significantly more than heavy wet snow per inch depth. Note that the density of snow increases as depth increases. The density of snow depends on whether it s fresh wet wind packed or mixed with ice.

People have been killed by snow avalanches sliding off roofs during big snow winters. If your roof is 1 000 square feet the total snow load is 15 000 pounds of snow. Dense than snow on the east coast which tends to be wetter and denser. If you re not sure which type to choose always settle for the wetter types as they are denser.

In 48 inch deep snow the design density is more than 2 4 psf per inch while the actual density is probably 1 5 psf per inch or more. Whether a roof can sustain a load without damage or collapse depends mainly on the depth and density of the snow as well as the depth and spacing of the rafters and trusses. The minimum roof pitch for shedding snow is around 30 or a 6 12 or 7 12 slope although this is not a definite as the material of your roof the direction of the snow and wind are some factors that can affect whether or not snow will slide as roofs of as little as 10 have been reported to shed snow. In part this is why it is important to prevent ice buildup on a roof structure.