Technical specification and use of chain drives on roof windows
Using electric chain drives on roof windows and skylights places higher demands on drive technology than vertically installed façade windows. This is mainly due to the changed kinematics and the static loads caused by the roof pitch and external environmental factors. Chain drives automate ventilation processes (natural ventilation) and ensure smoke extraction openings in smoke and heat exhaust ventilation systems (SHEV).
Building physics and structural characteristics
Unlike turn-and-tilt windows in the façade, where the drive essentially has to overcome the friction of the fittings and the sash weight along a vertical axis, different force vectors act on roof windows.
Load bearing and snow load
A chain drive on a roof window must lift the entire sash weight against gravity. In addition, the push force (N) of the drive must be dimensioned so that it can also handle external loads. These include in particular snow load in winter and wind load (suction and pressure). While 200 N to 300 N are often sufficient for a façade window, roof window drives often require push forces of 400 N up to 1000 N, depending on the area and glass weight.
Tight closing and wind tightness
Due to the exposed position on the roof, the contact pressure in the closed state is critical. The drive must have sufficient Holding force to compress the window seals enough to keep out driving rain and wind. If the locking force of the drive is too low, this can lead to moisture damage in the roof structure.
Function and design
Chain drives use a special back-stiff chain that bends in one direction (for winding into the housing) but remains rigid in the other (push direction).
Geometric adjustment with brackets
As roof windows are usually designed as top-hung or pivot sashes, the angle between the window frame and the sash changes significantly during opening. A rigidly mounted drive would create mechanical stresses that damage the chain or the mounting point. Therefore, mounting with swivel brackets is therefore essential. They allow the drive body to follow the movement of the window and keep the exit angle of the chain in line with the point of force application.
Stroke lengths and opening width
The stroke length (usually between 250 mm and 800 mm) determines the geometric free cross-section of the opening.
- Ventilation: For daily ventilation, strokes of 300–500 mm are often sufficient.
- RWA: Smoke extraction often requires larger opening angles to achieve the aerodynamically effective smoke extraction area (Aa value) in accordance with EN 12101-2. High-performance drives with strokes of up to 1000 mm are used here.
Electrical system integration
The choice of voltage level defines the field of application and the peripherals.
230 V AC (alternating current)
Drives with 230 V mains voltage are mainly used for pure comfort ventilation . They can be controlled directly via conventional ventilation switches or smart home actuators. No external power supply is required, which simplifies retrofitting.
24 V DC (direct current)
This is the standard for Smoke and heat exhaust systems (SHEVS) and professional building management systems. 24 V drives offer decisive advantages:
- Emergency power backup: With SHEV control panels with batteries, the drives remain operational even during a power failure (functional integrity).
- Precise control: Many 24 V drives feature BUS interfaces or intelligent load cut-off, enabling exact positioning and synchronisation (in tandem operation on wide windows).
Safety aspects
The automated operation of roof windows involves risks that must be minimised by technical measures.
Rain sensors
Because an open roof window can cause immediate water damage in the building during sudden rainfall, wind/rain detectors are mandatory. These sensors give the control unit a priority command to close immediately as soon as moisture is detected.
Anti-trap protection
Roof windows are often out of direct reach, but protection measures must still be observed where they are accessible (e.g. with low roof slopes). Intelligent drives continuously measure their current consumption. If it rises abruptly during closing (obstacle detection), the drive reverses to release the obstacle.
IP protection class
Due to the risk of condensation on the roof window or brief splash water when the window is open, drives for this application should have at least protection class IP 54 (protection against dust and splash water).
Mounting types and retrofitting
For installation on roof windows, a distinction is made between frame mounting and sash mounting; in the roof area, the drive is usually mounted on the fixed frame (top or bottom) and the chain bracket on the moving sash.
Specific mounting kits are often available for retrofitting common roof window types (e.g. from Velux, Roto or Fakro). Universal drives, on the other hand, require an individual check of the rebate depth and space requirements to ensure that the drive does not collide with the interior lining when the window is closed.
Suitable chain drives for roof windows
For roof windows and skylights, the right choice is the VS-KA chain drive with 250 to 1500 N, 24 V or 230 V and a stroke of up to 1000 mm. For very heavy sashes or humid environments, the VS-KA 2500 offers 2500 N and IP66 protection. Determine the right stroke length with our guide Calculate chain length. You will find all models under Chain drives – ab Lager Hamburg, Versand innerhalb von 24 Stunden.
Would you like to replace an existing drive from another manufacturer? In our guide Replacing window drives you will find suitable alternatives for GEZE, Aumüller and Kingspan STG.
Sources & further references
EN 12101-2: Smoke and heat control systems – Part 2 European standard defining the requirements for natural smoke and heat exhaust ventilators (NSHEV), including test procedures for drives under snow load and wind. URL: https://www.beuth.de
ZVEI e. V. – SHEV guideline Information from the German Electrical and Digital Industry Association on the design and installation of electric drives for smoke and heat exhaust ventilation systems. URL: https://www.zvei.org
DIBt – German Institute for Building Technology Information on building regulation lists and approvals for construction products in fire protection and ventilation technology. URL: https://www.dibt.de