Yes, and on a commercial roof an opening unit is often worth the extra cost. Electrically actuated rooflights are standard products from every manufacturer we fit, and they will ventilate a deep-plan space in a way side windows cannot, because warm air leaves at the highest point. Two things need settling before you order: whether you want comfort ventilation or life safety smoke ventilation, which are different specifications entirely, and whether there is power and a control route to the roof. The second question sinks more schemes than the first.
Comfort ventilation and smoke ventilation are not the same product
A comfort vent opens on demand or on a timer to move air through a space. A smoke vent opens automatically in a fire to clear smoke and heat, is part of a life safety system, and carries its own standards, actuation requirements, testing regime and certification. The hardware can look similar on the roof and the price is not similar at all.
Some units serve both duties, with the comfort function on a normal control and the fire function on a separate signal that overrides it. If your building needs a smoke vent, that requirement is set by the fire strategy rather than chosen from a brochure, and our page about smoke ventilation rooflights and AOVs covers it. This page is about ventilating for comfort.
Chain actuators, spindles and rack drives
Three mechanisms cover nearly all commercial opening rooflights. Chain actuators are compact, quiet and common on smaller units, pushing an articulated chain out of a housing to open the sash to perhaps 300mm to 400mm. Spindle or linear actuators give a longer, stronger stroke and suit heavier glazed units. Rack and pinion drives, often in pairs on wider units, handle the largest sashes and give the most open area.
Selection follows the sash weight and the opening angle wanted, and the manufacturers publish both. Pneumatic actuation still appears on older industrial smoke vents but is uncommon on new comfort installations. On a heavy unit two synchronised actuators are normal, and they must be matched, because one running ahead of the other will rack the frame.
Free area is the number that matters
An opening angle sounds impressive and tells you very little. What ventilates a space is the free area: the actual gap through which air can pass, quoted either as geometric free area, which is simply the measured opening, or as aerodynamic free area, which accounts for the losses caused by the shape of the unit and is always the smaller figure.
The distinction bites when a specification asks for a given area of ventilation and a supplier quotes the geometric figure. Compare like with like. On a 1200mm by 1200mm unit with a 400mm chain stroke, the useful area is a fraction of the glass area, so achieving a target usually means several units rather than one large one.
Night purge and getting heat out of a building
The strongest case for opening rooflights in a workplace is overnight cooling. A building that has absorbed heat all day into its floor slab and structure can be flushed through the small hours by opening high-level vents, so the fabric starts the next day cooler and the cooling plant works less or is not needed at all.
It works because of stack effect: warm air leaves at the top and pulls cooler air in at low level, so the arrangement needs a low-level inlet as well as the roof outlet. A run of opening rooflights with no way for air to enter the building will do very little. That has to be designed as a pair, and it is worth saying before somebody buys actuators expecting a result.
Rain sensors, wind speed and automatic closing
Any opening rooflight on a commercial building should close itself. A rain sensor on the roof, wired to the control panel, will drive every unit shut within seconds of the first drops, and that is the difference between a useful system and an expensive water ingress event on a Saturday.
Wind is the other input. High wind on an open sash loads the actuator and the hinges well beyond their design case, and an anemometer input closing the units above a set speed protects the hardware. Both sensors want positioning where they read genuine conditions rather than sheltered by a plant enclosure, and both need to be identified in the handover pack so they get checked.
Control panels, wiring and who does the electrics
Most commercial actuators run at 24V DC from a control panel fed from the mains, and the panel needs a position: accessible, dry, and near enough to keep cable runs sensible. From there, control can be a simple wall switch, a timer, a thermostat, or an interface into a building management system so the vents respond to internal temperature and CO₂ alongside the rest of the plant.
The electrical installation is a separate trade. We set the units, fit the actuators and run the cabling to an agreed point, and a qualified electrician makes the final connections, energises the panel and certifies the installation. That division wants agreeing at order stage so there is no gap in the middle of the programme, and so the roof is not finished with a wire hanging out of it.
Manual opening where power is a problem
Not every position justifies wiring. Manual options exist and work: a winding pole through a gearbox for units within reach of a floor below, a crank handle at a walkway level, or a manual stay on a low-level unit in a stair or a small office. They are cheaper, they need no panel, and they need nothing certified.
The limitation is honest. Nobody opens a manual roof vent at the top of a warehouse, so in practice manual units only ventilate where somebody can operate them easily and remembers to. Above a certain height, electric or nothing.
When an opening unit is the wrong answer
Where the building is air conditioned and sealed by design, opening rooflights fight the plant and waste conditioned air unless they are interlocked with it. Where the roof is fully exposed and the space is heated hard in winter, the extra seals and moving parts are a maintenance liability for a function that gets used a fortnight a year. And where the aim is purely daylight, a fixed unit is cheaper, better insulated and has nothing to fail.
We will tell you if a fixed unit is the better buy. Actuators, sensors and panels are the parts of a rooflight installation most likely to need attention in a decade, and there is no sense adding them where nothing will use them.
What we need to specify it properly
The volume of the space and its use, whether there is a low-level air inlet, whether the building has cooling, the distance from the proposed unit positions to the nearest suitable power supply, and whether anything has to interface with a BMS or an existing panel. With those we can put a range in an email, and a survey then fixes the price and the positions.
We install and replace rooflights across Oxford and twenty-five miles by road, fitting VELUX, Fakro, Keylite and Roto units, with a ten-year workmanship guarantee on the installation and fifteen years in the trade. Call 01865 704245 or email info@heritageskylightsoxford.co.uk.
Helpful reading on this
Costs, comparisons and the questions we are asked most.
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