Roof snow load calculator
Measure the depth of each layer and the roof’s footprint. Fresh, packed and icy snow weigh very different amounts.
Snow load
5.7 lb per sq ft
- Total weight on the roof
- 6,807 lb
- In tons
- 3.4 tons
- Roof footprint
- 1,200 sq ft
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How it works
Snow’s weight depends on how much water is in it. Following FEMA’s snow load guide, 10 to 12 inches of fresh snow holds about an inch of water, which weighs about 5.2 pounds per square foot. Old, settled snow is denser: 3 to 5 inches holds the same inch of water. Ice is denser still, about 4.75 pounds per square foot for every inch.
The calculator uses the middle of each range, adds the layers, and multiplies by the roof’s footprint, the area of the house seen from above, since that’s the area snow falls on.
Example
With fresh, fluffy snow 12 in, old, packed snow 0 in, ice 0 in, roof footprint length 40 ft, roof footprint width 30 ft, the answer is 5.7 lb per sq ft.
Tips before you buy
- Warning signs of too much weight include sagging ceilings or rooflines, new cracks in walls, doors that suddenly stick, and creaking or popping sounds. Get out and call a professional if you see them.
- Clear snow from the ground with a roof rake rather than climbing on an icy roof.
- Rain on top of snow adds a lot of weight quickly, because the snow soaks it up.
- Drifts collect against walls, chimneys and lower roof sections, so the load isn’t even. Check those spots first.
Common questions
How much does a foot of snow weigh on a roof?
Fresh snow is about 5 to 6 pounds per square foot per foot of depth. Packed, settled snow is about 15 to 16. A 1,200 square foot roof under a foot of fresh snow carries about 3.4 tons.
How much does an inch of ice weigh?
About 4.75 pounds per square foot, roughly the same as a foot of fresh snow.
How much snow can my roof hold?
It depends on where you live, since roofs are designed for local snow conditions. Your local building department can tell you the design snow load for your area.