Snow Load Calculator — Weight of Snow on a Roof & Should I Shovel?

Snow Load Calculator: Should You Shovel Your Roof?

Unless you're lucky enough to live in sunny California, you probably know the never-ending plight of shoveling heaps of snow from your roof every winter. Our snow load calculator helps you decide when to remove snow from your roof by comparing the actual weight of snow with the load-carrying capacity of your roof structure.

What Is the Weight of Snow on a Roof?

To calculate the weight of snow on a roof, you need to supply the following information:

• Roof length and width — Enter these values in feet (Imperial) or meters (Metric). If your roof is pitched, enter the length and width of the flat area covered by the roof.
• Roof pitch — Enter as a ratio x:12. For example, a 4:12 pitch means the roof rises 4 inches for every 12 inches of horizontal run. The calculator converts this to an angle to find the true sloped roof area.
• Snow cover thickness — The depth of snow on your roof in inches or centimeters, measured at the thickest point.
• Snow type — The density of snow depends heavily on its type. Fresh snow is fluffy and light, while ice is extremely dense and hazardous. When unsure, always select the wetter, denser type to stay on the safe side.
• Maximum allowable load — The load-bearing capacity of your roof, typically 20–30 lbs/ft² (0.96–1.44 kN/m²) in the US. Check your local building code or consult a structural engineer if unsure.

Snow Load Formula

The snow load (pressure per unit area) is calculated as:

snow load = snow density × thickness × g
Result in kN/m² (SI) or lbs/ft² (Imperial)

The total weight of snow on the roof accounts for the sloped area:

snow weight = (length × width / cos(pitch angle)) × snow load

The cosine factor adjusts the flat footprint area to the actual sloped roof surface. A steeper pitch means more actual roof area — but also means snow slides off more easily.

Snow Density Table

Fresh snow is soft, fluffy, and light. Snow that has remained on your roof for several days will settle — while the layer appears thinner, its weight barely decreases as the density increases significantly. Ice buildup is the most extreme case: its density is over 15 times higher than fresh snow and must be removed immediately.

Permissible Snow Load: USA (ASCE 7-16)

If you live in the US, the relevant standard is ASCE 7-16 (Minimum Design Loads for Buildings and Other Structures), published by the American Society of Civil Engineers. These standards have been updated since their first publication in 1988.

The maximum snow load your roof can safely carry depends primarily on your geographic location. Houses in Ohio or Minnesota must be built to handle much heavier snow loads than those in California. Typical design values range from 10 lbs/ft² (0.48 kN/m²) in warmer southern states to 100+ lbs/ft² (4.8+ kN/m²) in mountainous Alaska.

Other factors that affect the design snow load include:

• Terrain type — Open, windswept areas accumulate snow differently than sheltered urban locations.
• Roof exposure — Roofs blocked by trees or taller structures accumulate more snow.
• Building temperature — Unheated buildings (garages, barns) accumulate more snow than heated homes because heat loss through the roof does not melt snow from below.
• Building importance — Hospitals, power plants, and schools require higher safety factors.

Permissible Snow Load: Canada (NBC)

In Canada, the National Building Code (NBC) governs structural snow load design. Each province adopts the NBC with minor regional adjustments, so actual values may differ slightly from national figures. The standard uses a 1-in-50-year ground snow load as the characteristic design value.

Key factors considered under the Canadian code include:

• Roof exposure — Windswept or exposed roofs accumulate less snow; sheltered roofs accumulate more.
• Slipperiness of the roof surface — Snow slides off slippery metal or steep roofs, reducing the accumulated load.
• Building importance — Critical facilities require greater design loads.

Should I Shovel My Roof Today?

Based on the roof parameters you enter, the calculator displays:

• The actual snow load (pressure) on your roof in lbs/ft² or kN/m²
• The total weight of snow in lbs or kg
• A percentage of your maximum allowable load reached
• A recommendation: safe, caution, or shovel now

Warning Signs of Roof Stress

Even if the calculator shows a safe result, always watch for these physical warning signs:

• Creaking or cracking sounds from the roof structure
• Doors or windows that suddenly stick or are difficult to open
• Sagging ceiling tiles or drywall
• Visible bowing of roof rafters or trusses
• Water leaks appearing suddenly during cold weather (ice dam formation)

If you notice any of these signs, evacuate the affected area and contact a structural engineer or emergency services immediately.

Benefits of a Snow Cover

Not all snow on your roof is bad! A moderate snow layer actually provides insulation that reduces heat loss from your home. In regions with extremely cold temperatures, this can lower heating costs. The key is balance — a thin layer of settled snow offers insulation benefit, while a thick accumulation of heavy wet snow or ice poses serious structural risk.

How to Remove Snow from Your Roof Safely

• Use a roof rake from the ground whenever possible — avoid climbing onto a snow-covered roof.
• Work from the edges inward, removing snow in layers rather than trying to clear it all at once.
• Never use metal tools that could damage shingles — use plastic or rubber-edged roof rakes.
• Leave a thin layer of snow on the roof rather than scraping down to shingles, which can cause damage.
• Wear non-slip boots and use a safety harness if you must go on the roof.
• Clear gutters and downspouts to prevent ice dams, which can cause water to back up under shingles.
• Hire a professional roofing contractor for heavy accumulations or steeply pitched roofs.

Remember: Never wait until a roof is at the brink of failure. Shoveling proactively after a major snowfall is far cheaper than repairing a collapsed roof.