Roof Load Calculator: Dead, Snow, Wind & Live Loads
Calculate roof dead, live, snow, wind and rain loads in kN/m² and psf. Find ASCE 7 governing load combinations and structural capacity limits.
Roof Geometry & Environmental Design Loads
2.65 kN/m² · 477.9 kN Total Force
Equivalent to 55.5 psf (pounds per square foot). Total factored gravitational force on roof framing: 48.7 metric tonnes across 180 m² plan area.
Governing Design Load
Total Roof Force
Effective Snow Load
Wind Velocity Pressure
Roof Live Load
ASCE 7-16 Load Combinations
Values in kN/m²Gold bar highlights the governing structural load combination (1.2D + L + S).
Snow Slope Factor (Cs) vs Pitch
ASCE 7-16 shedding curveCurrent pitch: 22° yields Cs = 1.00. Roofs shed 100% of snow above 60°.
Structural Roof Vectors & Free-Body Diagram
Schematic cross-section illustrating gravity downward forces (Dead D, Snow S, Live L) and aerodynamic wind vectors.
ASCE 7 Itemized Load Combination Summary
Total factored roof load: 2.65 kN/m²| Combination Code | Engineering Description | Factored Pressure (kN/m²) | Imperial (psf) | Design Status |
|---|---|---|---|---|
| 1.4D | Dead Load Only | 0.63 | 13.2 | Sub-critical |
| 1.2D + 1.6(Lr or S or R) | Gravity & Snow Dominant | 2.39 | 49.9 | Sub-critical |
| 1.2D + 1.0W + L + 0.5S | Wind Pressure Interaction | 2.52 | 52.7 | Sub-critical |
| 1.2D + L + S | Combined Snow & Live Load | 2.65 | 55.5 | GOVERNS |
| 0.9D + 1.0W | Wind Uplift & Overturn | 0.85 | 17.8 | Sub-critical |
Variables Explained
D (Dead Load)
Permanent gravitational weight of all building materials composing the roof assembly (rafters, sheathing, insulation, tiles/shingles, ceiling drywall, and MEP fixtures).
L_r (Roof Live Load)
Temporary loads incurred during construction, reroofing, inspection, and maintenance by workers and staging equipment (nominally 0.96 kN/m² or 20 psf in ASCE 7).
S (Flat & Sloped Roof Snow Load)
S = 0.7 × p_g × C_e × C_t × I_s × C_s, where p_g is ground snow, C_e is exposure factor, C_t is thermal factor, I_s is importance factor, and C_s is slope reduction.
C_s (Roof Slope Reduction Factor)
C_s = min(1.0, max(0, (60 - pitch) / 30)). Steep roofs shed snow quickly: C_s = 1.0 for pitch ≤ 30°, tapering to 0.0 at 60°.
W (Velocity Wind Pressure)
q_z = 0.613 × K_z × K_zt × K_d × V² × I_w × 10^-3 (kN/m²), converting wind velocity V (m/s) into dynamic surface pressure.
Governing Design Load (U)
The supreme factored combination of dead, live, snow, and wind loads that controls the sizing of structural joists, rafters, and foundations.
Important Notes
Preliminary Engineering Reference: This calculator provides preliminary structural load estimates based on standardized ASCE 7 formulations. It does not account for complex roof geometry, unbalanced snow drifts against parapets, or aerodynamic wind vortex shedding at eaves and ridges.
Professional Licensure: Structural roofing modifications, solar array additions, or truss installations must be formally stamped and reviewed by a licensed Professional Engineer (PE) or Structural Engineer (SE) compliant with your local building jurisdiction.
Frequently Asked Questions
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Structural EngineeringQuick Tips
- 1Use appropriate units and conversion factors
- 2Consider safety margins in calculations
- 3Document your calculation assumptions
- 4Verify results with alternative methods