How to Calculate Roof Stress From Ice & Snow

Roofs on homes and commercial buildings are constructed to withstand a certain amount of ice and snow load. In areas that typically receive very little snow, such as in the southern United States, design snow load can be as low as 5 pounds per square foot. In places where snow is common in the winter, residences and commercial buildings can be rated for as high as 25 pounds per square foot. By knowing your roof’s snow and ice load, as well as how much snow has fallen, you can calculate roof stress.

Coffee can, 6-inch diameter
Ruler
Calculator

Instructions

- 1
  Collect a sample of snow to determine the water content with an empty 6-inch diameter coffee can able to hold 3 pounds of coffee beans. Fill the coffee can to the brim with snow from any location. Since the snow on the ground is the same density as that on your roof, there’s no need to climb onto the roof to collect a snow sample.
- 2
  Melt the snow by taking it inside for a couple of hours. When the can contains only water with no trace of snow, measure the depth of the water in the can with a ruler.
- 3
  Multiply the depth of the water by 5.2 to determine the snow load in pounds per square foot. For example, if the melted snow sample measures 3.5 inches, the stress on your roof from the snow is 18.2 pounds (5.2 x 3.5 = 18.2).
- 4
  Estimate the average thickness of ice on your roof under the top layer of snow. Do not attempt to chip ice from your roof because you don’t want to damage the shingles. Every inch of ice is about 92-percent water weight, so multiply the thickness of ice in inches by 5.
- 5
  Add the water weight from the ice to the snow moisture amount you already calculated to determine the roof stress from the ice and snow that has accumulated.

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