This professional-grade tool computes the flat roof snow load (pf) per ASCE 7 methodology and optionally the balanced sloped roof load using a user-provided Cs. Designed for structural engineers and plan reviewers, it prioritizes correctness, accessibility, and auditability.
Authoritative Data Source & Methodology
Primary reference: ASCE/SEI 7-22, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Chapter 7 (Snow Loads). Use the ASCE Hazard Tool for site-specific pg. All calculations are strictly based on the formulas and data provided by this source.
The Formulas Explained
Flat roof snow load:
\\[ p_f = 0.7\, C_e\, C_t\, I\, p_g \\]
Optional balanced sloped roof load:
\\[ p_s = C_s\, p_f \\]
Glossary of Variables
- pg: Ground snow load (site-specific).
- Ce: Exposure factor (terrain/obstructions).
- Ct: Thermal factor (roof heat loss/conditions).
- I: Importance factor (per Risk Category).
- pf: Flat roof snow load (computed).
- Cs: Sloped roof factor (depends on slope/surface/thermal conditions).
- ps: Balanced sloped roof load (if Cs provided).
How It Works: A Step-by-Step Example
Assume Imperial. Let pg = 30 psf, Ce = 1.0, Ct = 1.0, I = 1.0.
\\( p_f = 0.7 \times 1.0 \times 1.0 \times 1.0 \times 30 = 21 \text{ psf} \\)
If Cs = 0.9, then \\( p_s = 0.9 \times 21 = 18.9 \text{ psf} \\).
Note: Drift, sliding, unbalanced loading, rain-on-snow, and ponding require additional checks per ASCE 7-22 Chapter 7.
Frequently Asked Questions (FAQ)
Where do I get pg?
From the ASCE Hazard Tool or your AHJ’s published values.
Does this include drift/sliding?
No; this tool covers balanced flat/sloped roof loads only.
Which units should I use?
Select psf (Imperial) or kPa (SI). The tool converts consistently.
How do I choose Ce, Ct, I?
Per ASCE 7-22 and local amendments; consult a licensed engineer.
Why is Cs optional?
Cs applies to sloped roofs and depends on slope/surface/thermal regime.
Permit submittal?
Use as an engineering aid; sealed calcs may be required.