Updated: 07.11.2026
The Snow load is the weight of the snow lying on a roof window, skylight or glass roof. When opening, a window actuator must lift this load in addition to the Sash weight .
How large is the snow load?
Snow load is given in kilonewtons per square metre (kN/m²). In Germany, DIN EN 1991-1-3 with its national annex defines snow load zones. Depending on zone and altitude, the ground load is usually between 0.65 and just over 1 kN/m², considerably higher in mountain areas. On flat and slightly pitched roofs about 80 % of this value is used. Binding values for a building are provided by the structural engineer.
What does this mean for the actuator?
On a roof window the actuator at the opening edge carries about half of the load. A sash of 1.2 × 1.2 m with 0.5 kN/m² of snow adds about 350 N to the actuator – more than the glass itself weighs. In the Window actuator calculator you enter the snow load under the window type “roof window”.
Frequently asked questions
Should the window open at all when there is snow?
Usually not for ventilation. A wind/rain sensor or a timer prevents unnecessary opening. For smoke ventilation, however, the system must open even under snow load; this is specified by the specialist planner.
Is the snow load part of the reserve?
No. Snow is calculated separately, then the result gets the Reserve.
Read more
See also in the glossary: Shape coefficient (snow load) · Overhead glazing
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: RWA (smoke and heat exhaust ventilation system, SHEV) · Chain actuator · Continuous rooflight · Thrust
Datasheets and manuals · All terms in the glossary
