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Snow Load

Flat-roof snow is p_f = 0.7·C_e·C_t·I_s·p_g. The 0.7 accounts for wind scouring a flat roof; a sheltered roof loses that benefit, and a warm roof sheds snow above about 30°. Drifting against parapets and steps is a separate calculation and is usually what actually overloads a roof.

Ground snow load pg (kPa)

Exposure factor Ce

Thermal factor Ct

Importance factor Is

Roof slope (°)

Tributary area (m²)

Flat-roof snow pf

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Sloped-roof snow ps

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Slope factor Cs

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Load on the area

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Rough depth (fresh snow)

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Versus ground load

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Does not cover drift loads, sliding snow, rain-on-snow surcharge or unbalanced loading — drifting against a parapet or a taller adjacent roof is frequently the governing case and must be checked separately.

PRELIMINARY SIZING ONLY — not a code-compliant design check. These are first-pass equations; they omit member stability, local buckling, shear and combined-stress interaction, connections, second-order effects and jurisdiction-specific factors. Codes vary by country and edition. Structural design must be performed and sealed by a qualified engineer.