How is the design snow load on a roof calculated?

It is calculated using the formula S = µ × S0, where µ is the shape coefficient of the roof and S0 is the ground snow load (Clause 3.1).

What is the shape coefficient for roofs with an angle over 60 degrees?

The shape coefficient (µ) is 0, meaning no snow load needs to be considered as the snow will slide off.

Where can I find the ground snow load (S0)?

It should be obtained from local meteorological records; indicative values for specific Indian regions (like Shimla, Srinagar) are provided in Appendix A.

Do I need to combine maximum wind load and maximum snow load?

Load combinations are dictated by IS 875 (Part 5), but typically wind and maximum snow load are considered with appropriate combination factors, as strong winds often blow snow away from roofs.

IS 875 Part 4

: 1987

Design Loads (Other than Earthquake) for Buildings and Structures - Snow Loads

CurrentSpecializedCode of PracticeBIMStructural Engineering · Structural Design and Loading

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IS 875 Part 4 provides guidelines for calculating design snow loads on roofs and structures. It is primarily used by structural engineers designing buildings in high-altitude or snow-prone regions to ensure structural stability against snow accumulation.

Specifies snow loads to be considered in the design of roofs and other parts of buildings in snowy regions.

Quick Reference Values

Shape coefficient (µ) for roof pitch ≤ 30°0.8

Shape coefficient (µ) for roof pitch ≥ 60°0

Shape coefficient (µ) for roof pitch between 30° and 60°0.8 x (60 - pitch)/30

Key Formulas

S = µ × S0 — Design snow load on a roof area, where µ is the shape coefficient and S0 is the ground snow load

Practical Notes

Snow loads can generally be ignored for roof slopes greater than 60 degrees as snow typically slides off.

Ground snow loads (S0) must be determined based on local meteorological data or elevation, as it varies significantly by local topography.

Engineers must account for asymmetrical snow loading patterns on curved and multi-span roofs due to drifting, sliding, and wind effects.