Pounds
Snow load is the additional weight on a roof structure added by snow and ice buildup on the roof.
Calculating the snow load is crucial to determining if the structure can handle the snow’s
additional weight.
The ATC has a snow load hazard tool that can help you identify when a snow load presents a
hazard to the structure.[1] You can calculate snow load in a few easy steps.
The volume of snow on the roof directly relates to how much it will weigh. To find the snow volume, start by measuring the roof’s footprint.
We strongly recommend against walking on the roof to take these measurements for obvious safety
reasons. Instead, measure the length and width roof from the ground to find the footprint; we’ll
account for the pitch later. Keep all measurements in feet to simplify the formulas.
When you have the roof’s length and width as measured from the ground, multiply them together.
This will give you the area of the footprint. Alternatively, you can also use a volume
calculator to find this measurement.
If you measured from the ground and did not measure the roof’s actual dimensions, then it’s time
to account for the roof pitch. If you don’t know your roof pitch, then try our roof pitch
calculator to find it.
To account for the pitch, you’ll need to multiply the area by the multiplier for the given roof
pitch. You can find a list of multipliers on our roofing calculator. The calculator above
applies this formula. If the roof is a flat roof, then this step is not needed..
Before moving on, multiply the area by the snow depth in feet to find the volume of snow on the
roof.
Snow varies in weight depending on the density. Fresh powder weighs much less than wind-packed drifts. Check out our snow weight calculator to find the density of various types of snow.
The final step in calculating the snow load is to multiply the volume of snow on the roof by its density. If you have a density range, then multiply the volume by each part of the range separately to find the minimum and maximum snow load.