Updated: 07.11.2026
The Shape coefficient (μ) converts the snow load on the ground into the load on a roof. It depends mainly on the roof pitch: snow slides off steep roofs and stays on flat ones.
Values for simple roofs
| Roof pitch | Shape coefficient μ |
|---|---|
| 0° to 30° | 0,8 |
| 30° to 60° | decreases linearly from 0.8 to 0 |
| ab 60° | 0 |
Based on DIN EN 1991-1-3 with national annex. Other values apply to special cases such as snow drifts at higher parts of a building; these are determined by the structural engineer.
Example
Ground snow load 0.85 kN/m², skylight on a flat roof: 0.8 × 0.85 = 0.68 kN/m², i.e. about 680 N per m². A 1.2 × 1.2 m sash thus carries just under 1,000 N of snow, of which the actuator carries about half.
In the calculator
In Window actuator calculator you enter the snow load on the roof for the window type “roof window”, i.e. the value after applying the shape coefficient.
Read more
Tools: Calculate force and stroke with the Window actuator calculator, find the right model in a few questions with the actuator finder.
Not sure which actuator fits? Call us at 040 50694631 (Mon–Fri 8 am–5 pm) or use the actuator finder.
Related terms: Dome rooflight · Wind load
