Electric and opening rooflights in Cambridge, for light and fresh air

A hinged flat rooflight lifts on one edge, pushed up by a chain or spindle actuator on the opposite edge. It is the most common opening type on a flat roof: the frame stays compact, the glass sheds rain while it is part-open, and the gap it makes is exactly where you want it, at the top of the room. The limit is the stroke. A hinged unit usually opens by a few hundred millimetres at its free edge, so the clear area for air is a wedge rather than the full size of the glass. Our guide to hinged opening rooflights compares single-edge and ridge-hinged designs.

A sliding rooflight runs the whole glazed panel along rails over a fixed section of roof or a second glazed panel, leaving a large, open slot to the sky. It moves far more air than a hinged unit of the same size and turns a room into something close to a covered terrace on a hot day. It needs clear roof beside the opening for the panel to park on, a heavier frame and more careful weathering at the tracks. The guide to sliding rooflights covers the roof space they need and where they make sense in a terrace extension.

On a pitched roof, the opening unit is a roof window: centre pivot, top hung or a combination. A centre-pivot window turns on hinges at mid height, so the top half swings out and the bottom swings in, which is the usual choice for electric operation. Our answer on whether an electric skylight can go on a pitched roof explains the options, and the roof window installation service covers pitched roofs in full.

A roof access hatch is a hinged rooflight built to open wide, often to 90 degrees or more, so you can climb through to a flat roof to clean gutters, tend a green roof or reach a terrace. It is an opening rooflight first and a daylight source second, and it is sized around a person rather than the light. The guide to rooflight roof access hatches covers stair and ladder arrangements beneath.

For the question of how wide each type actually opens, and what that means for airflow and security, see how far an opening rooflight opens.

Flat opening rooflights are made in a run of standard sizes from around 600 by 600 mm up to about 1500 by 1500 mm and larger for sliding units, with made-to-measure sizes common. The glass size you see from below depends on the kerb and the plaster reveal, so a unit sold as 1000 by 1000 mm to its upstand shows a smaller square of sky inside. We draw the internal opening on the light plan so you can judge the size from the room, not from a brochure.

The clear opening matters for air. A hinged unit that lifts its free edge by 300 mm leaves a wedge-shaped gap; the effective free area is less than the length of the edge times the stroke, because the gap narrows towards the hinge. Manufacturers declare an equivalent or free area for their opening units, and that figure is the one to use when you want the rooflight to count towards purge ventilation. A sliding unit, by contrast, can give an opening close to its full glazed area.

Specification points we set down on the light plan for an opening unit:

• Frame: aluminium with a thermal break for most flat units, with a slim sightline so the frame does not eat the light.
• Actuator: chain or spindle, its stroke and its force, matched to the weight of the glass and the pitch of the kerb.
• Controls: wall switch, remote, rain sensor, and any timer or temperature control.
• Glazing: double or triple, low-E, solar control for the orientation, with a laminated inner pane for overhead safety.
• Blind: whether one is fitted now or later, and where its motor and cable will run. Opening units need a blind that clears the moving sash, which our guide to electric blinds for opening rooflights covers.
• Screen: an insect screen where the manufacturer offers one for that unit, useful in a bedroom or a kitchen by a garden.

Part L sets a limiting U-value of 2.2 W/m²K for a new or replacement rooflight in an existing home, now measured with the unit in the horizontal plane. Opening frames have more joints and seals than fixed ones, so a well-made opening unit is judged on its declared whole-unit figure. Our energy efficient rooflights service explains how glass and frame together make that number.

The actuator is a compact motor that drives a chain or spindle to push the glass open and pull it shut. It usually runs on 24V DC, supplied through a control unit that converts mains power. That control box sits somewhere accessible: in the ceiling void with an access panel, in a cupboard or in the loft. The rain sensor, the wall switch and the remote receiver all connect to it. Pitched roof windows with electric operation follow a similar pattern, with the motor and control built into the top of the frame. Our answer on whether electric rooflights are 24V or 230V explains which parts run at which voltage.

The mains connection is electrical work under Part P of the Building Regulations. Adding a fused spur to an existing circuit in a dry room is often not notifiable, while a new circuit, or work in the zones around a bath or shower, is. Either way the connection should be made by a competent electrician, and we arrange that as part of the installation. See does an electric rooflight need an electrician and the guide to wiring an electric rooflight for the detail, including cable routes in a flat roof build-up.

Where a mains supply is awkward to reach, for example on a finished extension where nobody wants a ceiling opened up, a solar powered unit is an option. A small photovoltaic panel on the frame charges a battery that drives the motor, and the controls are wireless. The range of solar units is narrower than mains ones, and the battery needs enough daylight to stay charged through a dull winter, which a flat roof in Cambridge usually provides. Our guide to solar powered roof windows covers where they fit and where they do not.

Controls range from a simple wall switch to a full home automation link:

• A wall switch by the door, the plainest and most reliable.
• A handheld remote, useful where one room has two or three units.
• A timer to open the glass on warm mornings and close it before you leave.
• A temperature or indoor climate sensor that opens the rooflight when the room passes a set point. See can a rooflight open when the room gets too warm.
• A link to a smart home system, voice assistant or app, depending on the manufacturer's range.

Smart control is only as good as its integration. Some rooflight systems connect through the manufacturer's own hub, some accept a simple relay input from a wider home system, and some do neither. We confirm what your chosen unit supports before it is ordered. The guide to smart home control for rooflights and the answer on controlling a skylight with Alexa go through the common arrangements, and can a rooflight open on a timer covers scheduled opening.

Running costs are small. The motor runs for well under a minute to open or close the glass, and the control unit draws a very low standby current the rest of the time. The answer to whether electric rooflights use much electricity puts that in context. Noise is similarly modest: a steady hum while the glass moves, then silence, as the answer on whether electric rooflights are noisy explains.

Stack ventilation relies on the difference in temperature between inside and out. Warm indoor air is lighter, so it rises and leaves through the highest opening, pulling cooler air in through lower ones. The taller the path between the low and high openings, the stronger the draw. That is why a rooflight at the top of a stairwell can cool a whole house on a still evening: the stair is a three-storey chimney, with the garden door or a ground floor window as the inlet. Our guide to stack ventilation with rooflights shows how to pair openings in a terrace, a semi and a new home with an open-plan ground floor.

Night cooling is where this pays off most in summer. After a hot day, the outside air often drops well below the indoor temperature by late evening. Opening the rooflight and a low window for a few hours flushes the stored heat out of the fabric of the room, so the next morning starts cooler. A timer or a temperature control makes that routine without anyone having to remember, and the rain sensor keeps it safe.

Approved Document F sets ventilation provisions for homes, including purge ventilation for clearing heat, cooking fumes or paint smells quickly. An opening rooflight can count towards purge ventilation where its free area, as declared by the manufacturer, is large enough for the room, and a Building Control officer will judge that against the drawings. It does not replace the continuous or extract ventilation the regulations ask for in kitchens and bathrooms, so a cooker hood and a bathroom extract fan are still needed.

A few room-by-room points:

• Kitchens: place the opening near the cooking zone but not over the hob, so steam and heat rise past it without the rooflight becoming a hot spot.
• Bathrooms: an opening rooflight clears steam fast after a shower; it sits outside the zones that limit electrical fittings only where its controls are placed correctly.
• Bedrooms in lofts: an opening unit on the cooler slope, often north or east, lets night air in without the morning sun pouring through an open sash.

Insects follow the air. Moths come to a lit rooflight on a summer evening, and a kitchen by a garden draws flies. Several manufacturers offer insect screens that fit inside the frame of an opening unit; the answer to whether opening rooflights let in insects explains which designs accept them.

Rooflights on houses usually fall under Class C of the permitted development rules, which allows alterations to a roof provided the rooflight does not project more than 150 mm beyond the plane of the roof slope and does not sit higher than the highest part of the roof. One condition matters particularly for an opening unit: a window on a side-facing roof slope must be obscure glazed and non-opening unless the part that opens is more than 1.7 metres above the floor of the room. A roof window low on a side slope of a semi, where you would stand to open it, can therefore fall outside permitted development. On a flat roof, the combination of an upstand and a raised opening frame can come close to the 150 mm limit, and where it is close we check the position with the planning authority before ordering.

Permitted development does not apply to flats and maisonettes. Across Cambridge and South Cambridgeshire, planning is run by Greater Cambridge Shared Planning, and the city alone has 18 conservation areas. Rooflights can still be permitted development in a conservation area unless an Article 4 direction removes the right, and listed buildings always need listed building consent. On a front slope in a conservation area, a flush-fitting conservation rooflight is often the expected approach, and several conservation units are available with manual or electric opening. Our conservation rooflight installation service covers those cases. You can check the constraints on your own address through the Greater Cambridge Shared Planning conservation area pages.

Building Regulations approval is a separate question. Cutting a new opening in a roof alters the structure, and the rooflight has to meet the thermal standard in Part L, so a new rooflight is normally notifiable, as the Planning Portal guidance on rooflights sets out. Other parts apply too: Part K for safety glazing overhead and for the reach of controls, Part B where a rooflight is near a boundary or a party wall, and Part P for the electrical connection. We make the Building Control notification where the work is notifiable, install to current Building Regulations and give you the completion paperwork at the end.

One point that comes up in loft conversions: an opening rooflight is not a smoke vent. Automatic opening vents for smoke control belong to communal stairs and commercial buildings, and a house relies on a protected escape route and, where needed, an escape window instead. Our answer on whether a rooflight can be a smoke vent in a house explains the difference, and the guide to electric rooflight safety features covers obstruction detection, child locks and the rest. Children and controls are covered directly in can children open an electric rooflight.

Before the day, the survey fixes where the rooflight goes and why, the unit and glass, the control route and the cable path. The written light plan and quote set all of that down, along with the Building Control notification if the work is notifiable. The rooflight is ordered to size, and we book the fitting once it is in hand.

1. Protection. Dust sheets go down inside, and the area under the new opening is cleared and screened.
2. Opening the roof. The covering is cut back, the opening is formed and any joists are trimmed with new timbers to carry the loads around it.
3. Kerb and weathering. The upstand is built or set, the covering is dressed up it and the roof is watertight again by the end of the first day.
4. Fitting the rooflight. The frame goes on the kerb, the actuator is fixed and set, and the sash is checked for an even close all round.
5. Controls. The control unit, rain sensor and switch or remote are connected, and the electrician makes the mains connection.
6. Inside. The reveal is insulated, boarded and plastered, with the cables hidden in the reveal and ceiling.
7. Handover. We run the rooflight through its full travel, test the rain sensor, show you the controls and any manual override, and leave the manufacturer's documents and the Building Control completion paperwork.

A roof window with electric operation on a pitched roof follows a similar sequence, with the tiles or slates stripped around the opening, the window set in the rafters and the flashing dressed in. The plaster in the reveal needs a few days to dry before decorating.

The installation is covered by our 10-year workmanship guarantee, alongside the manufacturer's own product warranty on the rooflight and its motor. For a sense of what drives the overall cost, from unit size to controls and electrical work, see skylight and rooflight costs, and for a home where the opening unit is part of a wider lantern design, see roof lantern installation. The Vision Skylights home page shows every service we install in Cambridge and the villages around it.