Snow Load Calculator: Calculate Roof Snow Load per ASCE 7-22
📍 US-focused accuracy | Free tool for homeowners, architects & builders. Estimate balanced roof snow load (psf) using ground snow data, exposure, thermal factor, and roof pitch.
Interactive Snow Load Calculator
Enter your project details below. The calculator follows the balanced load formula pf = 0.7 × Ce × Ct × Is × pg (ASCE 7-22).
How to calculate snow load on a roof: 2026 guide
Calculating snow load is essential for safe roof design, especially in regions with heavy snowfall. The snow load calculator above uses the ASCE 7-22 formula to convert ground snow load into roof load, considering exposure, thermal effects, importance, and roof slope. Whether you’re a contractor or a homeowner, knowing your roof’s snow load capacity prevents structural damage.
Ground snow load to roof snow load: the formula
Engineers use the following balanced snow load calculation: pf = 0.7 × Ce × Ct × Is × pg. Where pg is the ground snow load (psf) from local building codes. After computing pf, the sloped roof snow load becomes ps = pf × Cs, where Cs reduces load for steeper roofs (snow shedding).
Typical ground snow loads for US cities (ASCE 7-22 reference)
| City / Region | Ground Snow Load (psf) | Notes |
|---|---|---|
| Boston, MA | 35 psf | Coastal modified |
| Chicago, IL | 25 psf | Urban flat terrain |
| Denver, CO | 30 psf | Mountain influence |
| Buffalo, NY | 55 psf | Lake-effect zone |
| Minneapolis, MN | 50 psf | Heavy snow belt |
| Seattle, WA | 20 psf | Mild moderate |
| Portland, ME | 60 psf | Northern exposure |
💡 Pro tip: For your exact location, reference the ASCE 7-22 hazard tool or your local jurisdiction’s building department. Many counties provide interactive snow load maps.
Step-by-step snow load calculation example (2026)
Example: A heated house in Chicago (pg = 25 psf), exposure C (Ce=1.0), standard importance (Is=1.0), roof pitch 6:12 (≈26.6°).
- pf = 0.7 × 1.0 × 1.0 × 1.0 × 25 = 17.5 psf (flat roof snow load).
- Slope factor Cs for 26.6° (warm roof) = 0.85 → Sloped load = 14.9 psf.
- If roof area = 2,000 sq ft → total snow weight ≈ 29,800 lbs (≈ 14.9 tons). This helps size rafters or trusses.
Roof snow load safety checklist for 2026
- ✔️ Confirm your region’s ground snow load from updated maps (2026 codes).
- ✔️ Use correct exposure factor: B for sheltered, C for open, D for coastal.
- ✔️ Adjust thermal factor: unheated garages require higher load (Ct=1.1).
- ✔️ For low-slope roofs (≤15°), Cs = 1.0; for steeper roofs, use reduction.
- ✔️ Monitor snow accumulation: wet snow weighs ~20 psf per foot depth, ice heavier.
Snow drift load & special cases
Our calculator focuses on balanced loads, but roof steps, parapets, and adjacent higher roofs create snow drifts. For accurate drift loads (ASCE 7-22 Chapter 7), consider using engineering software. A rule of thumb: drift loads can be 2-3× the balanced load. For flat roofs with rooftop equipment, drifting is critical.
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Frequently asked questions (snow load)
Ground snow load (pg) represents the weight of snow on the ground. Use ASCE 7-22 maps, local building codes, or our table above. Many US cities publish pg values online.
Very accurate for typical residential roofs. However, localized drifting or ice dams may increase load. Always verify with structural engineer for final permits.
Yes. A 6:12 roof (26.6°) reduces load by ~15-20%; a 9:12 roof (37°) reduces by 40%+. Our calculator includes Cs factor per ASCE guidelines.
Absolutely. For flat roofs (pitch 0°), Cs = 1.0, and the sloped load equals the flat roof snow load. Ensure proper drainage and consider drift loads.
Balanced load is uniform; drift load is localized accumulation near changes in roof elevation, often higher. Our calculator provides balanced load — essential for general design.
Yes, we’ve implemented ASCE 7-22 coefficients and refer to 2026 hazard data. Where appropriate, we reference the latest code cycles.
Important disclaimer
This snow load calculator provides estimates for preliminary design only. Always consult a licensed structural engineer and refer to local building codes (including ASCE 7-22 amendments). TotalCalcHub is not liable for any decisions based solely on these results. Actual snow conditions vary.