Environmental Load
Roof Snow Load Calculator
Prepare roof snow loading for rafters, purlins, and roof beams by turning a ground snow load into a design area load, line load, total member load, and simple reaction estimate.
Snow Load Inputs
A typical balanced roof starter with neutral exposure, thermal, and importance factors.
Snow Load Summary
Factor summary
| Ground snow load | 1.20 kN/m^2 |
| 0.7 x Ce x Ct x Is x Cs | 0.7 x 1.00 x 1.00 x 1.00 x 1.00 |
| Total member snow load | 11.09 kN |
Calculation Basis
Assumptions & Limits
- Ground snow load and factors remain project assumptions and do not replace local snow-load mapping.
- The page prepares load inputs but does not apply full design combinations or code partial factors automatically.
- Changing tributary width, local peaks, or an uncertain load path require a more detailed model.
Reference Basis
Reference Snow Setups
| Best use | Roof snow load preparation before rafter, purlin, or beam checks |
| Primary output | Design snow load in kN/m^2 and converted line load in kN/m |
| Typical handoff | Area-load conversion, beam solver, roof member deflection checks |
| Model scope | Balanced snow preparation; drifting, sliding snow, and local accumulation are not automated |
Engineering Notes
- Use the governing ground snow load and factors from the project code basis or local authority data.
- The slope factor is explicit because roof angle, surface type, and snow retention assumptions can change the final load significantly.
- Drift loads at steps, parapets, valleys, and adjacent higher roofs can govern roof members and should be checked separately.
Calculation Method
- Flat roof snow: p_f = 0.7 C_e C_t I_s p_g. The calculator uses a transparent ASCE-style factor structure for preliminary balanced snow load preparation.
- Design snow load: p_s = C_s p_f. The roof slope factor adjusts the balanced flat-roof snow load.
- Line load: w = p_s x b_tr. The design area load is converted into beam line load through tributary width.
Frequently Asked Questions
- Can this page find the ground snow load from an address? No. Enter the ground snow load from the governing map, local authority data, or project design basis, then use this page for transparent factor conversion.
- Does this include snow drift loads? No. Drift, sliding, valley, and local accumulation cases need separate project-specific checks because they depend on roof geometry and surrounding obstructions.
- Why convert snow load into kN/m? Most beam and purlin checks need a line load. Tributary width turns the roof area load into the member input used by the beam solver.
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