Snow Load Calculator

Snow district

Roof pitch, degrees

House length in plan, m

House width in plan, m

Result

Load, kg/m²153
Load, kPa1.5
Pitch coefficient1
Snow on the ground, kPa1.5
Slope area, m²92.38
Snow in total, t12.24

Above thirty degrees the snow starts to leave

Calculates the snow load on a roof from the snow district and the pitch, in kilopascals and kilograms per square metre.

Snow load starts from the weight of snow on the ground in your district and is then adjusted for the roof. A shallow roof holds everything that falls; a steep one sheds it.

The coefficient is one up to thirty degrees, falls linearly to zero at sixty, and stays at zero above that. That single rule is why a steep roof needs far less timber than a flat one in the same place.

What this calculator shows

The load in kilopascals and in kilograms a square metre
The pitch coefficient and the ground snow load behind it
The area of the slopes and the total weight of snow on the roof

What to keep in mind

Districts follow the eight-zone scheme with ground loads from 0.5 to 4.0 kPa. If you know your local figure, read off the district with the matching value.
Drifts and snow bags behind parapets, valleys and dormers are not included. Those areas carry considerably more and are calculated separately in a real design.

FAQs

How much does snow weigh?

Fresh snow is around 100 kg a cubic metre, settled snow 200 to 300, and wet spring snow can pass 400. That is why depth alone says little about the load.

At what pitch does snow slide off?

It starts to matter above thirty degrees and is complete above sixty — on a smooth covering. A rough surface or snow guards keep it in place longer.

Does a snow guard change the load?

Yes, upward. It deliberately holds snow on the roof, and the design has to carry the full load as though the pitch were shallow.

Does the roof need clearing?

If the structure was designed for the district load, normally no. Clearing matters for valleys, for snow bags behind parapets and after an unusually heavy winter.

Worked example

A thirty-degree roof in district three

Input: district III, 30° pitch, a house 10 × 8 m in plan

Output: 153 kg a square metre

Note: That is 1.5 kPa with a coefficient of one, and about 12 tonnes of snow across the roof. At forty-five degrees the coefficient drops to 0.5 and the load halves.

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Snow Load Calculator

Result

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