Roof Snow Load Calculator
Calculate the weight of snow on your roof and whether it exceeds safe structural limits.
Know when to remove snow before it causes roof damage or collapse.
Roof snow load is the weight of accumulated snow pressing down on your roof structure. Excessive snow load is a leading cause of roof collapse in heavy snowfall regions.
Snow weight by type:
| Snow Type | Weight per Inch of Depth |
|---|---|
| Fresh powder (dry, light) | 3 lbs per sq ft per foot of depth (0.7 lbs/sq ft/inch) |
| Packed snow | 20 lbs per sq ft per foot of depth (~1.7 lbs/sq ft/inch) |
| Wet snow | 40 lbs per sq ft per foot of depth (~3.3 lbs/sq ft/inch) |
| Ice | 57 lbs per sq ft per foot of depth (~4.8 lbs/sq ft/inch) |
Formula:
Snow Load (psf) = Snow Depth (inches) × Weight per inch for snow type
Total Weight (lbs) = Snow Load (psf) × Roof Area (sq ft)
Safe limits:
Most residential roofs are designed to handle 20–40 lbs per square foot (psf) of snow load. A typical American home has a design load of 25–30 psf. Older homes and flat roofs may have lower limits.
Warning signs your roof is overloaded:
- Doors and windows that suddenly won’t open or close properly
- Cracking or popping sounds from the roof or ceiling
- Visible sagging of the roof deck
- Cracks appearing in interior walls or ceilings
- Leaning interior support posts
When to remove snow:
- When snow depth exceeds 12–18 inches on a flat or low-pitched roof
- When wet or icy conditions are present (wet snow is 4–5× heavier than powder)
- When snow has been on the roof for several days and compacted
- If you have an older home, flat roof, or have already had ice dams form
Safe snow removal:
- Use a roof rake from the ground — never climb on a snow-covered roof
- Start from the edge and work inward
- Clear a path directly below the roof before raking (falling snow is heavy)
- Do not chip ice directly off shingles — you can damage the roof
- Consider hiring a professional for steep or high roofs
Ice dams:
Ice dams form at roof edges when heat escapes through the attic, melting snow, which refreezes at the cold eaves. Water backs up behind the dam and can leak into the attic and walls. Prevention: improve attic insulation and ventilation.