Roof Snow Load Calculator
Estimate the weight of snow accumulating on your roof so you can take action before it becomes a structural danger to your home.
Calculate your roof snow load
Enter your roof dimensions, current snow depth, and snow type to see the estimated load on your roof.
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Fill in the fields above and click Calculate.
How to use this calculator
Enter the length and width of your roof's footprint (measure from the ground along the outside walls, do not attempt to measure on the roof itself), the current average depth of snow sitting on the roof in inches, and select the snow condition that best matches what you see. The calculator multiplies the roof area by the snow depth and the weight density of that snow type to estimate the total load in pounds and the load per square foot. Compare that per-square-foot figure against your roof's design load (check your home's building permit documents or ask a contractor) to gauge risk.
Tips for success
- Most residential roofs are engineered to handle 20–25 lbs per square foot, know your home's rating before a major storm.
- Measure snow depth in multiple locations and average them; depth varies widely across a roof surface.
- Wet spring snow can weigh 6–8 times more than fresh powder, never assume depth alone tells the whole story.
- Use a roof rake with an extension pole from the ground to safely remove snow rather than climbing onto the roof.
- Remove snow from the eaves first, then work inward to avoid creating a dam that traps meltwater under shingles.
Practical note
Understanding snow weight and roof capacity
- Fresh powder weighs roughly 3–7 lbs per cubic foot (about 1 lb per square foot per inch of depth), but it compresses quickly as more snow falls on top of it.
- Settled or packed snow, the most common condition mid-storm, averages around 20 lbs per cubic foot, equivalent to about 3 lbs per square foot for every inch of depth.
- Wet or heavy snow can reach 40+ lbs per cubic foot, meaning just 6 inches on a 1,200 sq ft roof can add over 33,000 lbs of force.
- Ice layers formed by melt-and-refreeze cycles are the most hazardous, they are nearly incompressible, transmit load with no give, and can cause sudden catastrophic failure.
- Most U.S. building codes in snow-prone areas require roofs rated for at least 20–30 psf (pounds per square foot) of snow load, but older homes and outbuildings may fall well below this.
- Roof pitch affects snow retention: low-slope roofs hold far more snow than steep roofs, which shed accumulation more readily.
Warning signs your roof may be overloaded
- Doors or windows that suddenly become difficult to open or close, a sign the frame is flexing under load.
- Creaking, cracking, or popping sounds from the ceiling or attic, especially during or after a storm.
- Visible sagging or bowing of the roof deck, ceiling, or rafters when viewed from inside the attic.
- Cracks appearing in interior walls or around door and window frames.
- Leaks that begin during or shortly after a snow event, which can indicate ice dams or a compromised roof deck.
FAQ
What is the average safe snow load for a residential roof?
Most modern U.S. homes built to current building codes in snow-prone regions are designed to support a ground snow load of 20–50 psf, which translates to a roof snow load (after accounting for pitch and exposure) of roughly 15–35 psf. However, this varies significantly by region, age, and construction type. Always consult your local building code or a licensed engineer for the specific rating of your home.
How do I measure snow depth on my roof safely?
Do not climb onto a snow-covered roof, it is extremely dangerous. Instead, use a long-handled roof rake to clear a narrow strip and measure the depth with a ruler or yardstick extended from the ground. Alternatively, if you have a single-story section or a porch roof you can safely reach, measure there and note that depth may vary on other sections. Take several measurements and average them for the most accurate result.
Should I use roof area or ground footprint area in the calculator?
Use the ground-level footprint (the length and width of the building's exterior walls), not the actual sloped surface area of the roof. Engineering snow load standards are calculated on the horizontal projected area, which is what this calculator uses. The pitch of the roof affects how much snow slides off, but the load is evaluated on the horizontal plane.
When should I remove snow from my roof?
A common guideline is to consider snow removal when accumulation reaches 6 inches of wet/heavy snow or 12+ inches of settled snow, or when the estimated load approaches 20 psf. However, the right threshold depends on your specific roof's load rating. When in doubt, remove snow conservatively, removing it in stages is safer for both you and the structure. Always use a roof rake from the ground rather than climbing up.
Does roof pitch affect the snow load?
Yes, significantly. Steeper roofs (typically 4:12 pitch or greater) shed snow more readily, so less accumulates compared to a flat or low-slope roof. The ASCE 7 standard used by engineers applies a "roof slope factor" that reduces the design snow load for steeper roofs. For this calculator we use the horizontal footprint area, which partially accounts for this, but a steep roof will naturally accumulate less than the depth you might measure on a flat surface nearby.
What should I do if I think my roof is in danger of collapse?
Evacuate the affected area of the home immediately, move people and pets out from under the stressed section or out of the building entirely. Do not attempt to go into the attic to check rafters if you hear cracking sounds. Call 911 if you believe collapse is imminent, and contact a licensed structural engineer or general contractor as soon as possible. Do not re-enter until a professional has assessed the structure.