Updated: 08.11.2026
In brief: On the flat roof of residential and office buildings, spindle actuators open rooflight domes and roof hatches for ventilation. Because the actuator has to lift the dome almost completely and snow lies on it in winter, it needs considerably more force than on a bottom-hung window. A rain sensor and wind monitor close the dome in bad weather.
What is different on a flat roof?
- High force: the dome lies horizontally; the force is about half its weight, plus reserve, see Thrust.
- Snow and wind: Snow load and Wind load act directly on the dome.
- Weather: rain falls straight in – a rain sensor is a must.
- Roof hatch: if the flap is also used to climb out, it must be possible to open it by hand at any time; this is clarified with the manufacturer of the flap.
Which actuators are suitable?
Spindle actuators again VS-LA (600–5000 N, IP65) or the VS-SA 2500 are the norm. Small, light domes can also be opened by a strong chain actuator. For large domes we plan two actuators with Synchronous control. Calculate the force with the Window actuator calculator.
steering
- Switch in the room below the dome or a VS-C24-7A ventilation control unit for up to 7 actuators.
- Rain sensor and Wind monitor on the roof.
- Smoke exhaust via rooflights is a separate topic and is planned project-specifically with an approved SHEV control panel.
For industrial halls: Retrofitting rooflights in halls. For a quote, send photos and dimensions via the Project enquiry.
Frequently asked questions
How much force does an actuator for a rooflight dome need?
Roughly half the dome weight in newtons, plus 50 % reserve for snow and wind. A dome weighing 40 kg therefore needs about 320 N.
Can I retrofit an existing rooflight?
Usually yes, if the frame and upstand offer space for actuator and bracket. Photos and dimensions are enough for an initial assessment.
Do I need 24 V or 230 V?
For ventilation with control unit and sensors, usually 24 V. More in the guide 24 V or 230 V.
Technically reviewed by Dietmar Heiken, Sales, Vent Systems HDI GmbH, Hamburg – around 20 years of industry experience. Questions? Phone +49 40 50694631 or info@ventsystems.de
Last updated: 08.11.2026
