When people talk about the 'load' a structure can take, they are basically talking about the weight or force a building can take before it starts to collapse.
The two main elements that put pressure on a structure once erected are wind and snow. Wind force is measured in speed, typically MPH (Miles Per Hour). Snow force is measured in pressure, typically PSF (Pounds per Square Foot).
If someone says that a structure has a wind load of 100 MPH with a snow load of 0 PSF, what they mean is that the structure can withstand up to 100 MPH winds and suffer no damage if there is no snow sitting on top of the building.
How strong are 100 MPH winds? See below for a basic breakdown:
Windspeed of 74-95 MPH = Category One Storm
Windspeed of 96-110 MPH = Category Two Storm
Windspeed of 111-129 MPH = Category Three Storm
Windspeed of 130-156 MPH = Category Four Storm
Windspeed of 157 MPH or greater = Category Five Storm
If someone says a structure has a wind load of 90 MPH with a snow load of 10 PSF, what they mean is that the structure can withstand up to 90 MPH winds and suffer no damage if there is a snow weight of 10 PSF sitting on top of the building.
How much snow is 5 PSF? See below for a basic breakdown:
Fresh snow: 10 to 12 inches of fresh snow is equivalent to about 5 PSF of roof space.
Packed snow: 3 to 5 inches of old snow is equivalent to about 5 PSF of roof space. A depth of more than 30 cm of snow may be greater than your roof can support.
Ice: A 1 inch layer of ice is equivalent to 12 inches of fresh snow.
Below is an overview of the WorkShell wind and snow loads. These are based on two framework setups - one is our standard framework, the other has additional roof supports that are fixed easily to the existing framework. A full structural calculations report for the tests listed below are available on request.
SETUP ONE - PASSED
Snow Load: 0 PSF
Wind Speed (3-second gusts): 100 MPH
SETUP TWO - PASSED
Snow Load: 10 PSF
Wind Speed (3-second gusts): 90 MPH
SETUP THREE - PASSED (reenforced framework)
Snow Load: 35 PSF
Wind Speed (3-second gusts): 100 MPH
SETUP FOUR - PASSED (reenforced framework)
Snow Load: 0 PSF
Wind Speed (3-second gusts): 160 MPH