Snow loads are influenced by elevation general weather and moisture patterns slope direction exposure roof or trail bridge configuration and wind direction and severity.
Snow load profile on roof.
A great deal of confusion currently exists among engineers architects recreation specialists and maintenance personnel concerning the proper snow loading to use for the design and maintenance of trail bridges building roofs and other structures in mountainous high snow load areas.
Once the ground snow load at the building site is determined it must then be converted to roof snow loads according to asce 7 with appropriate treatment of exposure to wind thermal properties of the roof roof slope unbalanced snow loads drifting and risk exposure.
If your roof is 1 000 square feet the total snow load is 15 000 pounds of snow.
The flat roof snow load is calculated using formula 7 3 1.
As snow melts and refreezes a layer of ice may sit under a foot of fresh snow to make the snow load weigh around 10 pounds per square foot.
Light fluffy snow may only weigh about seven pounds per cubic foot.
Table r301 2 1 climatic and geographic design criteria ground snow load.
You can shovel out a cubic foot of snow from the roof place it in a container and quickly weight it on a scale.
The weight of snow varies greatly.
Thus snow weighing 10 pounds per cubic foot and at a depth of 18 inches on a roof is exerting 15 pounds of pressure per square foot.
Loads increase on roofs as fresh snow becomes packed and new snow falls.
Basing on the roof parameters you specified in the first section our snow load calculator displays the maximum allowable snow cover thickness and snow weight.
The snow load that is applied to our structure is not the ground snow load but in most cases the flat roof snow load.
Your roof may be supporting 60 pounds per square foot of roof when snow and ice accumulate on the surface.
Roof snow and wind loads are based on the historical records for a given location however the local building authority should always be consulted to determine the correct roof snow and wind load to use for a given site and application.
Then measure the depth of snow on the roof and multiply it by the weight of a cubic foot of that snow.
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.
Other considerations for sloped roofs can be found throughout chapter 7 of asce 7 10.
Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off.
If unbalanced snow loading isn t required or specified the truss designer may enter the 25 psf snow load as a top chord live load tcll set the load duration factor to 1 15 for snow and turn snow loading off completely.
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.
