Advanced Snow Load Calculator
Use this estimator for planning only. Local code data and engineering review are still required for construction decisions.
Formula Used
The calculator uses a practical roof snow load workflow with user controlled factors.
Pf = 0.7 × Ce × Ct × Is × Pg Ps = Cs × Pf Design load = max(Ps, Ps × unbalanced factor) + drift + rain Measured load = (snow depth ÷ 12) × snow density + ice thickness × 4.76 Total load = final roof snow load × roof area Safety margin = allowable capacity - final roof snow load
Where Pg is ground snow load, Pf is flat roof snow load, and Ps is sloped roof snow load.
How to Use This Calculator
- Enter the project name, location, roof area, and allowable capacity.
- Select design mode for code style factor checks.
- Select measured mode for actual depth, density, and ice checks.
- Enter exposure, thermal, importance, slope, drift, and rain factors.
- Press Submit to view results above the form.
- Use CSV or PDF download buttons for project records.
Example Data Table
| Scenario | Pg | Ce | Ct | Is | Cs | Drift | Area |
|---|---|---|---|---|---|---|---|
| Small storage roof | 25 psf | 1.00 | 1.00 | 1.00 | 1.00 | 0 psf | 900 sq ft |
| Exposed farm building | 35 psf | 0.90 | 1.10 | 1.00 | 0.95 | 6 psf | 1,600 sq ft |
| Critical utility roof | 45 psf | 1.10 | 1.20 | 1.10 | 1.00 | 10 psf | 2,400 sq ft |
About This Cornell Snow Load Calculator
This Cornell Snow Load Calculator helps builders estimate roof pressure from ground snow, roof shape, and site conditions. It is made for planning checks, early sizing, and field notes. It does not replace a stamped structural design. Snow load rules depend on local maps, adopted codes, and professional judgment.
Why Snow Load Matters
Snow can look light, yet it may add a large uniform load. Wet snow, packed layers, ice, and drifting can raise pressure quickly. A flat roof can collect snow differently from a steep roof. Valleys, parapets, upper roofs, and wind shadows may create local surcharge zones. These areas often control member checks.
Main Calculation Ideas
The design mode starts with ground snow load. The calculator applies exposure, thermal, importance, and slope factors. It then adds optional drift, rain, and unbalanced load allowances. The measured mode uses depth, density, and ice thickness. It gives a field estimate of actual pressure on the roof surface. Both modes also calculate total roof weight from entered area.
Interpreting Results
The roof snow load is shown in pounds per square foot. The total load is shown in pounds and tons. A safety margin appears when you enter allowable roof capacity. A positive margin means the entered capacity is above the calculated load. A negative margin means the estimate exceeds that capacity. That result needs urgent professional review.
Good Input Practice
Use local ground snow data from the building authority or project documents. Choose conservative factors when the roof is exposed, cold, important, or prone to drifting. Measure snow depth in several places. Use heavier density for wet or compacted snow. Add ice separately because ice is dense. Keep photos and notes with each calculation.
Construction Use
This tool is useful during design conversations, maintenance planning, agricultural building reviews, and emergency screening. It can export CSV and PDF records. The example table gives typical entries for quick testing. Always confirm final loads with the code adopted in your location. For best records, save one report for design assumptions and another for measured storm conditions. Separate reports make later comparison easier. They also help owners see how changing slope, drift, or density changes the final load value safely.
FAQs
What is a roof snow load?
Roof snow load is the snow pressure supported by a roof. It is usually expressed in pounds per square foot. It can differ from ground snow load because roofs have slope, heat, exposure, and drift effects.
Is this an official Cornell tool?
No. This is an independent estimator for a Cornell snow load style topic. It is made for planning and education. Confirm all design values with local code documents and a qualified professional.
What is ground snow load?
Ground snow load is the mapped snow pressure expected on open ground. Designers use it as a starting value before applying roof factors. Enter the value required by your local authority.
What snow density should I enter?
Use a measured or conservative density when possible. Light dry snow is lower. Wet or packed snow is higher. If conditions are mixed, use a higher value for a safer estimate.
How do I include drifting?
Enter an added drift surcharge in psf. Use it for parapets, step roofs, valleys, obstructions, or wind shadow areas. Drift zones often need separate checks from the main roof field.
Why does roof area matter?
Area converts pressure into total weight. A 30 psf roof load over 1,000 square feet equals 30,000 pounds. This helps estimate total demand on framing and supports.
Can this check an existing building?
It can support an early screening check. It cannot confirm existing capacity by itself. Existing buildings need member sizes, materials, connections, age, damage, and code history reviewed.
Does roof slope reduce snow load?
Slope may reduce retained snow, but not always. Surface type, heat loss, sliding hazards, obstructions, and code limits matter. Use the slope factor only when it is justified.