Roof snow load calculator
Measure the depth of each layer in centimetres and the roof’s footprint. Fresh, settled and icy snow weigh very different amounts.
Measuring in feet and inches? Use the US version
Snow load
30 kg per m²
- In kilonewtons
- 0.29 kN/m²
- Total weight on the roof
- 2.4 tonnes
- Roof footprint
- 80 m²
How it works
Snow’s weight depends on how dense it is. Fresh, fluffy snow weighs about 100 kg per cubic metre, so every centimetre adds about 1 kg per m². Older, settled snow is about 250 kg per cubic metre, and ice about 917. The calculator adds up the layers, gives the load per square metre (and in kN/m², the unit engineers use), and multiplies by the roof’s footprint.
Example
With fresh, fluffy snow 30 cm, old, settled snow 0 cm, ice 0 cm, roof footprint length 10 m, roof footprint width 8 m, the answer is 30 kg per m².
Tips before you buy
- Warning signs of too much weight include sagging ceilings or rooflines, new cracks, doors that suddenly stick, and creaking. Get out and call a professional if you see them.
- Clear snow from the ground with a roof rake rather than climbing onto an icy roof.
- Rain on top of snow adds weight quickly because the snow soaks it up.
- Drifts pile up against walls, chimneys and lower roof sections, so the load isn’t even.
Common questions
How much does 30 cm of snow weigh on a roof?
About 30 kg per square metre if it’s fresh, or 75 kg per m² if it has settled. On an 80 m² roof, that’s 2.4 to 6 tonnes.
How much does a centimetre of ice weigh?
About 9.2 kg per square metre.
What snow load are roofs designed for?
It depends on where you live and the altitude. In low-lying parts of the UK, around 0.6 kN/m² (about 60 kg/m²) is common for houses. Your local building control can tell you what applies.