Ventilating atriums and light wells: using the stack effect with rooflights and window actuators

Updated: 08.11.2026

In brief: Warm air rises in the atrium. If you open rooflights or roof windows at the top and windows or flaps at the bottom, the air flows through the building by itself – the stack effect. Electric actuators open both sides together, by temperature, time programme or switch.

How the ventilation works

• Supply air at the bottom: windows or flaps on the ground floor.
• Exhaust air at the top: Rooflights, roof windows or a Continuous rooflight.
• The higher, the stronger: the air movement increases with the height between supply and exhaust air.
• Summer: Night cooling via the atrium cools the adjoining rooms.

Which actuators are suitable?

• Top: Spindle actuators again VS-LA (600–5000 N) for rooflight domes and heavy roof sashes; Rack and pinion actuators for long continuous rooflights.
• Bottom: Chain actuators again VS-KA for bottom-hung and top-hung sashes.
• From a sash width of about 1.5 m, two actuators with Synchronous control.

Calculate the force required for roof sashes with snow load with the Window actuator calculator; background in the guide Snow and wind load.

steering

• Supply and exhaust air together via a ventilation control unit or the building management system.
• Wind monitor and Rain sensor close the roof openings first.
• Smoke exhaust via the atrium is a separate topic and is planned project-specifically with an approved SHEV control panel.

Frequently asked questions

Is it enough to open only the rooflight?

No. Without supply air at the bottom, hardly any air flows in. Only openings at the bottom and top together use the stack effect.

What happens when it rains?

A rain sensor closes the roof openings automatically; lower windows can stay open if they are sheltered.

Can existing rooflights be retrofitted?

Usually yes. How it works is shown in the guide Retrofitting rooflights.