What is a stairwell AOV?
A stairwell AOV is an automatic opening ventilator (AOV) which provides at least 1.0m² of free area when open.
The installation is always located at the highest point in an evacuation stairwell and can take a number of forms.
Easivent has written a comprehensive guide on stairwell smoke ventilation systems which you can download here.
The most common types of stairwell ventilators are:
- Roof windows
Most stairwell ventilators are mounted on the roof of the stairwell. The type of roof will determine what ventilator is best:
The most common application of stairwell AOVs is installation on a flat roof, generally using a hatch vent. The ventilator will either be provided with a roof curb for building into the roof or it will be mounted onto a builder’s work upstand.
Ideally, roof upstands should have a slight pitch of 3-5 degrees to help prevent rainwater collecting on the ventilator which could be thrown into the building when opened. In specifying the roof upstand dimensions it is important that sufficient tolerance is built in to allow for the weathering membrane and an allowance for expansion.
Louvred ventilators may be installed onto a pitched roof. This type of roof and ventilator is commonly found in large industrial buildings containing firefighting staircases. They can also be used in small single-stair buildings with slate or tiled roofs.
Ideally the ventilator should be positioned at the ridge of the roof with the top flange tucked under the ridge flashing.
If the ventilator is down slope from the ridge then it is recommended that the top flange is extended to the ridge with additional panels to ensure a weatherproof seal.
Ventilators can satisfactorily be built into patent glazing by designing the vent to replace a pane of glass and selecting a flange of the same depth as the glass.
More detail on each of the above roof types is available in Easivent's quick guide to Stairwell AOVs.
Under the Construction Products Regulations (CPR) it is a legal requirement to use only certified products for smoke ventilation. For more information see SCS Group's Technical Bulletin here.