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Snow Load Calculator

Work out snow load instantly with clear inputs, formula shown and shareable results.

About Snow Load Calculator

Roof snow load starts from the ground snow load and applies three modifiers: 0.7 for the general reduction from ground to roof, exposure for wind scour and thermal for heat loss through the roof. A slope factor then reduces the load further above 30 degrees, falling linearly to zero at 70 degrees as snow slides off.

Formulas

Flat roof load

pf = 0.7 x Ce x Ct x pg

Sloped roof load

ps = Cs x pf, Cs = 1 - (slope - 30) / 40 for slopes above 30 degrees

Worked example

With the default values below, Snow Load Calculator returns Design sloped roof snow load of 1.050. Change any input above and every figure here is recalculated in your browser.

Inputs used

Ground snow loadminimum 0.05 kPa
1.5 kPa
Roof slopeaccepts 0–70 °
30 °
Exposure factor Ceaccepts 0.7–1.3
1
Thermal factor Ctaccepts 0.8–1.3
1

Results

Design sloped roof snow load
1.050 kPa
Flat roof snow load
1.050 kPa
Slope factor Cs
1.0000
Equivalent load
107.1 kg/m²

Step by step

  1. 1Values used
  2. 2Flat roof load
  3. 3Sloped roof load
  4. 4Design sloped roof snow load= 1.050 kPa
  5. 5Flat roof snow load= 1.050 kPa
  6. 6Slope factor Cs= 1.0000
  7. 7Equivalent load= 107.1 kg/m²

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Snow loads including drift, sliding and unbalanced cases must be established by a qualified engineer to the loading code in force.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Snow loads including drift, sliding and unbalanced cases must be established by a qualified engineer to the loading code in force.

Frequently Asked Questions

How is the Snow Load figure worked out?

pf = 0.7 x Ce x Ct x pg. Roof snow load starts from the ground snow load and applies three modifiers: 0.7 for the general reduction from ground to roof, exposure for wind scour and thermal for heat loss through the roof.

Does drifting need a separate check?

Yes. Snow accumulating against a parapet, a step in roof height or an obstruction can be several times the balanced load, and codes give specific drift surcharge shapes for it.

What values do I need to enter?

This calculator takes 4 inputs: Ground snow load, Roof slope, Exposure factor Ce, Thermal factor Ct. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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