How do I find my ground snow load zone?

The UK is divided into snow load zones in BS EN 1991-1-3 National Annex. Southern England is Zone 1 (0.30 kN/m²), the Midlands Zone 2, Northern England Zone 3, and Scotland Zones 4–5. The base value is then adjusted for altitude.

How does altitude affect snow load?

Snow load increases with altitude per BS EN 1991-1-3 UK National Annex: sk = sk,0 × [1 + (A/916)²] where A is altitude in metres. At 300m in Zone 2: sk = 0.40 × [1 + (300/916)²] ≈ 0.44 kN/m². The correction is non-linear (quadratic).

What is the shape coefficient for snow on pitched roofs?

The shape coefficient (μ1) reduces snow load on steeper roofs because snow slides off. For pitches up to 30°, μ1 = 0.8. Between 30° and 60°, it reduces linearly. Above 60°, it’s zero (no snow retention).

What is drift loading?

Drift loading occurs where snow accumulates against obstructions like parapet walls, changes in roof level, or adjacent taller buildings. Drift loads can be significantly higher than the uniform snow load and must be checked separately.

Is this calculator for structural design?

This calculator provides indicative snow loads based on BS EN 1991-1-3 for preliminary assessment. For structural design, always consult a chartered structural engineer who will consider all load combinations and safety factors.

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Roof Snow Load Calculator — BS EN 1991-1-3

Calculate roof snow loads to BS EN 1991-1-3 using UK ground snow load zones, altitude adjustment and shape coefficients by pitch.

Snow ZoneUK ground snow load zone

Site Altitude

Metres above ordnance datum

Roof Pitch

Angle of roof slope

Roof Span

Wall-to-wall span

Roof Length

Length of building

How We Calculate This

This calculator applies the BS EN 1991-1-3 (Eurocode 1) method for determining snow loads on roofs in the UK.

The formula

s = \u03bc1 × Ce × sk

Where: s = roof snow load, \u03bc1 = shape coefficient, Ce = exposure coefficient, sk = ground snow load

sk = sk,0 × [1 + (A / 916)²] (UK NA, A = altitude in metres)

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.