Roughly half a pound per square foot per inch of fresh powder, about 1.5 for settled snow, 2.5 for packed snow and around 5 for ice. Twelve inches of packed snow is about 30 pounds per square foot. Depth alone tells you very little — the type matters far more.
The Snow Load Calculator returns the design snow load on your roof in pounds per square foot using the ASCE 7 method. Enter the ground snow load for your region (from local building code maps, typically 20-100 PSF), exposure category (B, C, or D), thermal factor, and roof slope, and the tool returns the design roof snow load. Steeper roofs and warmer roofs shed snow faster and carry less load. Critical for sizing rafters, trusses, and structural sheathing in cold climates.
Snow load is a weight per square foot on the roof, and what matters structurally is not how deep the snow is but what it weighs. Fresh powder and old compacted snow of the same depth differ by a factor of four or more.
| Snow type | Per inch of depth | 12 inches | 24 inches |
|---|---|---|---|
| Fresh light powder | ~0.5 lb/sq ft | 6 lb/sq ft | 12 lb/sq ft |
| Settled snow | ~1.5 lb/sq ft | 18 lb/sq ft | 36 lb/sq ft |
| Packed / old snow | ~2.5 lb/sq ft | 30 lb/sq ft | 60 lb/sq ft |
| Ice | ~5 lb/sq ft | 60 lb/sq ft | 120 lb/sq ft |
These are planning approximations. A layer of ice under snow, or rain falling onto an existing snowpack, adds weight far faster than depth suggests — which is why the dangerous days are often the warm wet ones after a storm rather than during it.
Use a roof rake from the ground rather than going up. Clear in layers rather than scraping to the deck, which damages shingles. Work evenly across the roof — taking all the snow off one side of a gable leaves an unbalanced load, which is its own problem. And never use a ladder against a gutter loaded with ice.
Roughly half a pound per square foot per inch of fresh powder, about 1.5 for settled snow, 2.5 for packed snow and around 5 for ice. Depth alone tells you very little — the type matters more.
It depends on what the roof was designed for, which comes from the local ground snow load. As a practical warning, doors that suddenly stick, new ceiling cracks and visible sagging all mean stop and get it looked at.
Use a roof rake from the ground, clear in layers rather than scraping to the deck, and work evenly across both slopes. Going up onto a snow-covered roof is how people get hurt.
The snowpack absorbs the rain, so the load rises sharply with no change in depth. The heaviest roof loads of a winter are often on a warm wet day after a storm rather than during the storm itself.