Free online roof snow load calculator based on the ASCE 7 standard. Enter ground snow load, roof slope, and environmental factors to calculate the design snow load. Switch between psf and kN/m² units, with a full step-by-step calculation breakdown.
ASCE 7 Standard · Runs Locally⚙️ Input Parameters
📖 About Snow Load Calculation
What Is Snow Load?
Snow load is one of the environmental loads that must be considered in structural design. It represents the downward pressure exerted by accumulated snow on a roof surface. Accurate snow load calculation is critical for structural safety, especially in regions with heavy snowfall.
ASCE 7 Calculation Method
The American Society of Civil Engineers ASCE 7 standard provides the standard method for snow load calculation:
- Flat roof snow load: pf = 0.7 × Ce × Ct × I × pg
- Sloped roof design snow load: ps = Cs × pf
- Slope factor Cs: For heated buildings, Cs=1.0 up to 30°, decreases linearly from 30° to 70°, and is zero above 70°
Factor Definitions
- Ce (Exposure Factor): Reflects wind exposure. Fully exposed Ce=0.9 (wind blows snow off), sheltered Ce=1.2 (snow accumulates)
- Ct (Thermal Factor): Reflects roof insulation. Heated buildings melt snow faster, Ct=1.0; unheated Ct=1.1-1.2
- I (Importance Factor): Higher building categories have stricter safety requirements. Hospitals and essential facilities use I=1.2
Important Notes
- This tool is for preliminary design estimates. For formal design, consult the complete ASCE 7 standard
- Ground snow load pg should be obtained from local building codes or ASCE 7 snow load maps
- Unbalanced snow loads, drift loads, and other special conditions require additional calculations
- Results are for reference only and do not replace professional structural engineering judgment
❓ Frequently Asked Questions
What is the difference between roof snow load and ground snow load?
Ground snow load pg is the pressure of snow on the ground. Roof snow load is the design value after applying exposure, thermal, and importance factors. For flat roofs, the roof snow load is typically about 70% of the ground snow load. Sloped roofs will have even lower values.
At what roof slope does snow load become zero?
Per ASCE 7, the slope factor Cs drops to zero at 70°, meaning no snow load needs to be considered. For heated buildings, the reduction begins at 30°. For unheated buildings, it begins at 45°.
How do I convert between psf and kN/m²?
1 psf ≈ 0.0479 kN/m², and 1 kN/m² ≈ 20.89 psf. This calculator supports one-click unit switching, with all inputs and results converted simultaneously.
Where can I find the ground snow load for my area?
In the United States, refer to the ASCE 7 ground snow load map or your local building code. Other countries have equivalent resources in their national building standards.
What building types is this calculator suitable for?
It is suitable for preliminary snow load estimation of typical flat and sloped roof buildings. For complex roof shapes (multi-level roofs, skylights, parapets, etc.), additional drift and accumulation loads must be considered. Consult a licensed structural engineer for detailed design.