How do I calculate roof snow loads per ASCE 7-22?

ASCE 7-22 Chapter 7 provides the snow load procedure. Start with ground snow load (pg) from maps. Apply exposure factor (Ce), thermal factor (Ct), and importance factor (Is). For sloped roofs, apply slope factor (Cs). Flat roof snow load: pf = 0.7CeCtIs pg. Sloped roof: ps = Cs pf.

What are the exposure categories for snow loads?

Fully Exposed (Ce = 0.8): Open terrain, no obstructions. Partially Exposed (Ce = 0.9): Some trees/buildings nearby. Sheltered (Ce = 1.0): Dense trees/buildings within 10× building height. Exposure reduces snow accumulation due to wind scouring. Lower Ce = less snow on roof.

How does roof slope affect snow loads?

Flat roofs (≤5°): Cs = 1.0 (full snow load). Low slopes (5-30°): Cs decreases linearly from 1.0 to 0.7. Steep slopes (>70°): Cs = 0 (snow slides off). For 30° slope: Cs ≈ 0.7. For 45° slope: Cs ≈ 0.5. Steeper roofs shed snow, reducing design load.

What is the minimum snow load requirement?

ASCE 7-22 requires minimum roof snow load: pm = Is × 20 psf for pg ≤ 20 psf, or pm = Is × pg for pg > 20 psf. This ensures roofs can handle light snow even in low-snow regions. Always check minimum vs. calculated load—use the higher value.

How do thermal factors affect snow loads?

Thermal Factor (Ct): Cold/Unventilated (Ct = 1.0): Normal conditions. Cold/Ventilated (Ct = 1.1): Well-ventilated attics increase heat loss. Warm (Ct = 1.2): Heated buildings with R-value < 30. Higher Ct = more heat loss = more snow melting = lower snow accumulation.

What is the importance factor for snow loads?

Importance Factor (Is) by Risk Category: Category I: Is = 0.80. Category II: Is = 1.00. Category III: Is = 1.10. Category IV: Is = 1.20. Higher importance = higher design snow loads for critical structures like hospitals, emergency facilities.

Snow Load Calculator

ASCE 7-22 Chapter 7Snow LoadsRisk Categories I-IV

ASCE 7-22 Chapter 7Snow Loads

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Enter ground snow load, exposure conditions, and roof geometry to calculate design snow loads.

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Snow Load Calculator

Frequently Asked Questions

01How do I calculate roof snow loads per ASCE 7-22?

02What are the exposure categories for snow loads?

03How does roof slope affect snow loads?

04What is the minimum snow load requirement?

05How do thermal factors affect snow loads?

06What is the importance factor for snow loads?