Electric rooflight installation in Crawley, with air on demand

An opening rooflight is a window in the roof that lets the room breathe as well as see. An electric one does the lifting for you, from a wall switch, a remote or a sensor, and shuts itself when rain starts.

Warm air rises. That is the whole argument for putting an opening pane at the highest point of a room. A loft bedroom in July, a kitchen extension with the oven on, a stairwell that holds the heat of the whole house: each has a ceiling where the stale, warm air collects, and a rooflight that opens lets it out. Air is pulled in from a window or door lower down to replace it, and the room changes its air without anyone opening three windows and propping a door.

The second job is light, which any rooflight does. A fixed pane brings it in and stops there. An opening one brings it in and gives you the choice of a sealed, quiet room or a ventilated one. That choice matters more than it sounds, because the same hole in the roof that lets out the heat will, when open, let in whatever is outside. Around Crawley that can mean aircraft on the Gatwick routes, the M23 and A23, the Brighton main line through Three Bridges, or simply a garden with a lawnmower in it. We plan the opening with that in mind, and we write it down in the quiet spec that comes with every quote.

How a rooflight opens decides how much air moves, how much rain it can shed and whether you can step through it. Hinged, sliding and hatch types are three different tools, not three price points.

A hinged rooflight lifts along one edge, like a cold frame. It is the simplest opening on a flat roof, it takes a standard-sized kerb, and its actuator is small. The opened pane also acts as a little shield against the prevailing wind, which matters for rain and for noise, since the gap faces away from the direction you choose. Its limit is the opening angle. A hinged pane opens to an angle, not flat, so the clear gap is smaller than the glass. The guide to hinged or sliding: choosing an opening rooflight puts the two side by side.

A sliding rooflight is a different animal. A glazed leaf travels on rails over a fixed leaf, and the opening is the area that the moving glass uncovers. For a roof terrace it is the answer. You can walk through it, stand under open sky, and pull it closed behind you. Sliding units reach sizes that no hinged pane can, which is why they appear over stairwells that lead to a terrace and over big kitchen extensions. Two questions come up every time, and both have their own pages: how big a sliding rooflight can be and whether a sliding rooflight is watertight when closed. The short answer to the second is that the seals and the drainage channels are designed for it, and the fitting details do the rest. For terrace access in particular, see sliding rooflights for roof terrace access.

The control is how the rooflight lives in a household. A well-placed switch gets used every day, and a rain sensor closes the pane when nobody is home to do it.

The simplest control is a wall switch with two buttons, up and down, placed near the light switches where a hand already goes. Next comes a handheld remote, which is useful when the rooflight is over a room where you sit, a conservatory or a garden room, and the switch is across the far side. A wall-mounted keypad adds a code, and a few products take commands from a phone. The page on controls for electric rooflights: switches, remotes and keypads covers them properly, and the answer on whether an electric skylight can work with Alexa or Google Home describes what a voice link needs in practice.

A rain sensor is a small plate on the roof, close to the rooflight, with a heating element that keeps it dry in fog and frost. The moment water touches it, the plate sends a signal, and the control unit closes the pane. It is the feature that gives an electric rooflight its special appeal. You leave the house in the morning with the window open for the day, and a shower comes through at eleven. The pane is shut before the first carpet fibre is damp.

An opening rooflight needs more roof detail than a fixed one. The upstand, the fall of the roof and the space for the sash to swing all affect how it performs, and how quietly.

A flat roof is never perfectly level. It needs a fall so that water runs off, and current guidance points to a fall of 1:80 as a minimum finished result. A rooflight on a kerb interrupts that flow, so the roof is built to carry the water around it. The upstand, the vertical face of the kerb above the finished roof, is usually set at a minimum of 150mm for water to stay out. A hinged rooflight that opens wide can need more, because a rain splash on the opened pane should not reach the gap. The answer to does an opening rooflight need a taller upstand covers the detail.

Size is a second question. An opening pane weighs what the glass weighs, and a large acoustic laminated unit is heavy. The bigger the pane, the stronger the hinges, the stronger the motor and the stronger the kerb that carries them. Sliding units hide their weight in the rails, which is why the size answer for them is different. The roof must also take the load. If the rooflight replaces a section of joists, the opening needs trimming with a header, and a structural engineer or the extension builder confirms that. We work to their detail.

People come to us with a rooflight that is stuck, or a fixed one that they wish opened. Both are replacement jobs, and both can be done neatly.

A sash that no longer opens may have a worn hinge, a failed seal or a motor that has come to the end of its life. A rooflight that has lost its seal might be misted as well, and for those our misted and failed rooflight replacement page is the place to start. The better-value route is often to renew the whole unit, since a new sash in an old frame means matching a product that may no longer be made. A fresh unit brings a current glazing build, a fresh seal and a motor with a known life. The page on how long an electric rooflight motor lasts explains what to expect.

A fixed rooflight that you wish opened is the other case. Sometimes the kerb and the frame can stay, and only the glazed part changes. More often the unit is replaced, because the sash, the hinges and the motor have to work together. If the glass is in good order and the frame is stock, there may be a route to fit a hinged sash and a motor within the existing opening. The page on converting a fixed rooflight to an opening one sets the options out.

The best electric rooflight is the one chosen for its room. Four rooms come up again and again, and each has a different answer.

A loft bedroom, often a 1950s or 1960s house with a dormer or a rooflight in the sloping ceiling, wants a roof window with a good seal and a quiet motor. It is the room that hears early flights and late arrivals, so the glazing build is the first decision, and the night-time opening habits are the second. A kitchen extension wants a hinged or sliding rooflight over the cooking and eating space, with a rain sensor, since the kitchen is where a window is easily left open and forgotten. A stairwell wants height and reach, which is where a motor earns its keep. A home office wants ventilation without distraction, which suggests a controlled, slow opening and a closed pane for calls.

Crawley's homes give these rooms a familiar shape. The New Town neighbourhoods, from West Green in 1949 to Maidenbower in 1987 and Forge Wood from 2014, are full of semis and terraces where the loft was converted or the back was extended. The Victorian terraces of northern Southgate, the concrete houses of Northgate and the terraces and flats of Bewbush each pose a slightly different roof question, and the survey finds the right answer for each.