01The short version
Opening to let air in is a different job from clearing smoke
A rooflight that opens and a rooflight that works as a smoke vent can look alike from the floor. They are built, tested and signed off for different purposes.
Plenty of people ask us whether the electric skylight they are about to buy can double up as a smoke vent. It is a fair question, because the motor, the chain and the opening sash look much the same. The answer is that an ordinary opening rooflight is not a rooflight smoke vent, and you should not treat it as one.
A smoke vent, often called an AOV (automatic opening vent), is a fire-safety product. It has been tested as a complete system, it is supplied with the right controls and power backup, and it is installed to a defined design. When an alarm or smoke detector triggers it, it opens by itself and lets smoke leave the building so people can get out and firefighters can see what they are doing. An opening rooflight sold for ventilation was never put through that process.
The two products can share a manufacturer and even a frame style. What separates them is the certification, the controls and the design behind them, not the way the glass looks.
Opening rooflight
Opens on a wall switch, remote or app. Made for fresh air, cooling a hot room and letting in daylight. Closes again when it rains if a sensor is fitted. Not a fire-safety product.
Smoke vent (AOV)
Opens automatically when a fire alarm system or smoke detector signals it. Tested and certified for that duty, with a defined opening area and a backup if the mains fails. Designed in as part of the building's fire strategy.
02Where they are used
Where a real smoke vent turns up
Smoke vents belong mostly to flats, shared stairs and commercial buildings, and the people who specify them are not the roofer.
The classic place is the top of a common stairwell in a block of flats. If there is a fire, the stair is the escape route, so smoke has to be kept out of it or drawn away. A vent at the head of the stair, linked to detectors, is one way of doing that. You also see them in offices, shops, schools and other commercial buildings where the fire strategy calls for smoke clearance.
On an ordinary house, a smoke vent is not normally part of the picture. A two-storey semi in Basildon relies on smoke alarms, the escape routes and the usual Building Regulations for fire safety. A rooflight on a landing or a kitchen-diner roof is there for daylight and air, and that is how it should be sold.
- Shared stairwells and lobbies in blocks of flats
- Corridors and atria in offices and public buildings
- Warehouses and units where the fire strategy asks for smoke clearance
- Any building where a fire engineer has specified one for a particular reason
That last item always comes from a written design, never from a guess. If your project is on that list, the vent is chosen and signed off first, and the rooflight order follows from it.
03What to ask
Who decides, and what to ask them
Whether you need a smoke vent is not our call, and it is not a supplier's. A fire engineer or Building Control decides.
The rules sit in the fire safety part of the Building Regulations and in the fire strategy for the building. For a flat block or a commercial unit, that strategy is written by a fire engineer or the responsible designer, then checked by Building Control. They set out whether smoke ventilation is needed, how big the opening has to be, and how it is triggered.
If you manage a block, own a shop or are converting a building to new uses, ask that person or body before you buy any rooflight. If the answer is yes, you need a product that carries the right test evidence and a control system to go with it. If the answer is no, you are free to choose an ordinary opening rooflight for the reasons you actually want one.
- Say what the building is and how it is used, including any flats above or below.
- Ask the fire engineer, designer or Building Control whether smoke ventilation is part of the fire strategy.
- If yes, get the vent specified in writing, with its certification and controls.
- If no, choose an opening rooflight for ventilation and daylight.
- Keep every document, because a later buyer or insurer may ask for it.
04Fitting
What this means for the rooflight you want
If you only want fresh air and light, an opening rooflight is the right tool, and it should still keep the heat in.
Most enquiries about opening units are for plain reasons: a stuffy first-floor landing, a kitchen that gets hot, a loft room that needs a cooler summer. For all of those, an electric or manually opening rooflight does the job well. We cover the motor, the controls and the rain sensor on our pages about how electric rooflights work and ventilating with opening rooflights.
Opening does not mean cold. The glazing has a warm-edge spacer, the frame ties into the roof insulation, and the sash shuts onto a seal that stops draughts once the heating is on. The same room that gets fresh air in July stays comfortable in January.
Escape is a separate question again. A roof window used as a way out of a room no more than 4.5m above ground has its own size and height rules, which we explain in can a roof window be a fire escape. Whether you can make an existing fixed unit open is covered in can a fixed rooflight be made to open.
Our free survey and written quote cover the opening unit you want. If a smoke vent is part of your building's design, we fit around what the fire engineer has specified. Have a look at electric opening rooflights for the full range.
A motor and a sash do not make a smoke vent. Test evidence, controls and a fire engineer's sign-off do.
Smoke, escape routes and the rules: where people get tangled
Does my house need a smoke vent?
An ordinary house does not normally need one. Smoke alarms, protected escape routes and the standard fire safety rules do that work. If your building is a flat, a block with a shared stair or a commercial unit, ask a fire engineer or Building Control.
Can I buy a skylight that is also a smoke vent?
Yes, certified smoke vent products exist, but they are a separate product with their own controls. They are specified for the building, so the choice comes from the fire strategy and not from a showroom brochure.
Will an electric rooflight open if the fire alarm goes off?
Not unless it has been designed and wired as a smoke vent. A standard electric rooflight responds to its own switch, remote or sensor. Do not rely on it in a fire.
Who checks a smoke vent installation?
Building Control, working from the fire engineer's design. For an ordinary opening rooflight in the roof of a house, replacing the whole unit is a notifiable controlled fitting under Part L, and we handle that notification for you. Our guide to whether rooflights need Building Regulations explains it.
