AOV and smoke ventilation systems, explained and installed.

An AOV, or automatic opening vent, is a roof or wall vent that opens on its own the moment a fire alarm signal reaches it, usually within seconds. Once open it lets smoke and heat escape upward and outward instead of filling the stairwell or corridor people need to use to get out. It is not there to put the fire out, it is there to keep the exit route usable while people leave.

Any residential block with a single common stair, which covers most UK apartment buildings, has no second way out if that stair fills with smoke. Approved Document B and BS 9991 both require a mechanism to keep the stair and its lobbies clear, and for most single-stair blocks that is a smoke ventilation system built around one or more AOVs. Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for the building has to keep it maintained, tested and documented, not just installed once.

The equipment

AOV rooftop vent	Louvred or polycarbonate dome, sized to a calculated free area rather than an off-the-shelf size.
Smoke dampers	Open on the fire floor, stay shut elsewhere, so smoke draws from one floor at a time.
Louvres	Wall-mounted alternative to a roof vent, used for car parks and plant areas.
Smoke shafts and risers	Fire-rated duct to the rooftop vent; natural systems rely on its buoyancy, so sizing and position matter.
Actuators	Chain or linear motors that physically open a vent or damper, wired back to the panel.
Control panels and detection	Decide which vents and dampers open and in what sequence, and flag a fault if one fails.
Break glass override	Lets the fire service open the vents by hand on arrival, regardless of automatic detection.
Weather sensors	Where fitted, balance smoke clearance against wind and rain; never override a genuine fire signal.

AOV, damper or louvre

An AOV is the vent itself, the opening smoke passes through to leave the building. A smoke damper is a valve inside the ductwork that decides where the smoke is drawn from, open on the fire floor and shut everywhere else. A louvre is a fixed or motorised grille set into a wall, used where venting through a wall suits better than venting through the roof. When someone reports "the AOV isn't working" the actual fault is just as likely to be a stuck damper or a jammed louvre actuator, so a proper service checks the whole chain.

Natural or mechanical

System	How it works
Natural	Hot smoke rises through a shaft under its own buoyancy, no fan. Fewer moving parts, suits most low and mid-rise blocks with a straightforward stair.
Mechanical	Fans pull smoke out where a natural shaft cannot be built large or straight enough: taller blocks, deep-plan buildings, basement car parks. More equipment, more to maintain.
Car parks	Enclosed and underground car parks trap vehicle fire smoke with no natural escape route, so these usually run on jet fans or ducted mechanical extract, sized separately from the residential system above.

Standards and legal duty

BS 9991	Sets when a smoke control system is required, by the building's height, storeys and stair arrangement.
Approved Document B	Building Regulations fire safety, works alongside BS 9991 for means of escape.
EN 12101-2	Standard for natural smoke and heat exhaust ventilators, what the rooftop AOV vent itself has to meet.
EN 12101-3	Standard for powered smoke and heat exhaust ventilators, for fan-driven mechanical systems.
RRO 2005	Responsible person's duty to keep the system maintained, tested and recorded, not just installed once.

A vent or fan without the right EN 12101 certification should not go into a life-safety smoke control system, whatever else it looks like on paper.

What we do

We design the smoke ventilation strategy against BS 9991, then supply, install, commission and maintain the shaft, vents, dampers, detection and control panel as one coordinated scheme, all in-house. We work with equipment from SE Controls and other established manufacturers, matched to the building rather than one fixed product line. For an existing system with no clear history we run a takeover survey and bring it up to standard before it moves onto a maintenance contract.

We cover apartment blocks, mixed-use developments, student accommodation, HMOs, offices and car parks, national from our West Midlands base, with a core area under the areas we cover. Ongoing compliance runs under planned AOV servicing and testing, with every visit logged. Where a building also needs detection and alarm work, we design and install fire alarm and detection systems as one coordinated, commissioned scheme alongside the smoke control.