Ask people why they want a skylight and they say light. Ask them a month after a hot spell and many say air. A room under a roof collects heat. The sun hits the roof, the ceiling warms, and the warm air rises and sits at the top of the room, which is exactly where nothing can get out. An opening rooflight puts a vent in that spot. It does the job a window on the wall cannot, because a wall window is the wrong height. Read on if you live in Leicester or Leicestershire and are eyeing an opening rooflight or roof window. We cover how the ventilation works, which rooms gain most, what purge ventilation means, and what to settle before the quote. It is general trade knowledge. How it plays out in your roof comes from the free survey.
Why a roof vent behaves differently
Warm air is lighter than cool air. Inside a room it rises and collects under the ceiling. Open a window low down on a wall and you move some air, but the warm layer sits above the window and stays put. Open something at the very top and the warm air has a way out. Cooler air from outside is drawn in lower down, through a door or a wall window, to replace it. Builders call this the stack effect, and it is the reason old houses had high vents and tall chimneys.
A rooflight, whether a skylight in a pitched roof or a flat-roof unit on a kerb, is a vent at the top by default. That is the whole case for choosing one that opens. A fixed rooflight lets the light in and leaves the heat where it is. An opening one lets the heat out. Which is why a loft bedroom with a fixed rooflight can feel like a greenhouse in July, and the same room with an opening one can be a room you want to sleep in.
For the stack effect to work, the air has to have somewhere to come from. Open a rooflight in a sealed room and not much happens. Open a door or a wall window on the shaded side as well and the air starts to move. This is the single most useful habit we can pass on, and it costs nothing.
A vent at the top only works if there is another opening lower down for fresh air to come in.
What purge ventilation means
You will hear two words used for ventilating a home: background and purge. Background ventilation is the small, steady flow that keeps a house from going stale. It comes from trickle vents, extract fans and gaps designed in on purpose. Purge ventilation is the opposite end: a big, fast change of air that you switch on when you need it, after painting, after a burnt dinner, or on a hot afternoon when the room has become a heat trap. An opening rooflight is a purge device. You open it wide for a while, the room clears, you close it.
Ventilation in new homes and in many changes to existing ones is covered by Part F of the Building Regulations, with guidance in Approved Document F. The government's page describes volume 1 as covering the ventilation requirements for dwellings. If your project is an extension or a loft conversion, the Building Control body will want to see how the new room is ventilated, and an opening rooflight is one of the ways that can be done. The details depend on the room and the design, so we do not quote a size from memory here. The official document is on gov.uk: Approved Document F, ventilation. Where the work is notifiable, the Building Control notification is something we handle for the roof installation, and the ventilation approach is raised with the survey.
The broader regulation picture for rooflights, including planning, is set out in skylight planning permission and building regulations.
Which rooms gain most
The rooms that benefit are the ones where heat and moisture build up and where a wall window cannot do the job on its own.
| Room | What it clears |
|---|---|
| Loft bedroom | Heat under the slope |
| Kitchen extension | Cooking heat and steam |
| Bathroom or shower room | Moisture and steam |
| Stairwell or landing | Warm air from the whole house |
| Open-plan living space | Solar heat from glass |
Loft bedrooms
A loft conversion has the least wall and the most roof, so it is the room most likely to overheat. A roof window that opens is usually the main source of air in that room. Placing it so you can reach it from the bed is a nicer design choice than it sounds, and the question of whether a roof window can ever be an escape route is a different one, and the answer sits on the roof window fire escape page.
Kitchen extensions
A flat-roof extension with a lot of glass and a hob in the middle collects every bit of cooking heat and steam. A flat-roof skylight or an opening panel in a lantern lets it escape above the cook rather than across the room. Extractor hoods deal with grease and smell at source. The rooflight deals with the general warmth that is left over.
Bathrooms and utility rooms
Moisture is the enemy in a small room with no window on an outside wall. A sun tunnel will not open, but a small roof window will, and it gives the steam a way out. This also helps with condensation on the room's surfaces, because damp air that leaves does not settle on cold glass or on the ceiling.
Stairwells
A rooflight at the top of a stairwell is a chimney for the whole house in summer. Opening a door below and the rooflight above can pull a noticeable draught through the house. Putting the unit out of reach is common here, which is the main reason people choose an electric one. The wiring and control side of that is in electric rooflights: wiring, controls and rain sensors.
How wide it opens, and which way
Opening rooflights do not all open in the same way, and the difference changes how much air you move and how safely.
A top-hung roof window hinges at the top and swings out from the bottom, like a small awning. It gives a natural position for ventilation with some rain protection. A centre-pivot window turns about its middle, so the bottom edge swings out and the top swings in. It opens wide for cleaning and for a large gulp of air. The two behave differently in the room, and top-hung or centre-pivot roof window goes through the choice.
Flat-roof units are different again. A hinged one lifts at one edge, usually the lower, and an actuator holds it at the angle you choose. A sliding or two-part unit moves a section across, which can suit an access hatch more than a vent. If you also want to get onto the roof, take a look at hinged or sliding access rooflight.
An important point about the amount of air. A rooflight that opens a hand's width is a gentle vent. One that opens wide is a purge. Some designs deliberately limit the opening for safety or security. If purge air is the aim, tell us at the survey so the product is chosen for how far it opens, and not only for its glass size.
Ask how far it opens, not only how big it is. Glass size and opening size are different numbers.
Keeping the rain out and the security in
The reasonable worry about an opening rooflight is what happens when you forget it. Rain gets in, or someone else does.
For rain, the answer is a restrictor, a rain sensor, or the habit of closing it. A top-hung roof window will usually shed light rain in its ventilation position. A rain sensor on an electric unit closes it when water arrives, as set out in do electric rooflights close when it rains. A night latch or vent position lets you leave a small gap with the unit locked against being pushed wider.
For security, a rooflight is above head height almost everywhere, but a flat roof over a single-storey extension can be reached from the garden. Locks, restrictors and laminated glass all matter in that case. A restrictor limits the opening so that it can be left on the vent setting without leaving a gap a person could use. These are the sort of details to decide at the survey, with the roof in view.
Children are the other consideration. A rooflight in a bedroom or a landing, within reach, should open in a way that is safe for the age of the people using the room. A restrictor is the usual answer. Electric control from a wall panel also lets an adult decide.
Choosing between manual, pole and electric
The choice is about reach and routine. If you can reach the handle comfortably, a manual unit is simple and has nothing to go wrong. If it sits high, a pole or a crank can work, though a pole is a thing that goes missing. If it is out of reach, or you want it to open and close on a schedule or in response to weather, electric makes sense.
Questions to settle before ordering
- Can you reach it, or does it need a pole or a motor?
- How wide does it open, and is that enough for purge air?
- Where does the replacement air come from?
- Is there a vent position that can be left on at night?
- How is it kept out of reach of children and intruders?
- Does the room also need an extractor fan for steam or cooking?
If the rooflight you have is fixed and you wonder whether it can be made to open, can a fixed rooflight be made to open sets out what is and is not possible. The answer turns on the unit and its frame, and we inspect both before giving you a yes or a no, so you are not guessing from a photograph.
Heat gain is a separate problem
Ventilation takes heat out. It does not stop the sun putting it in. On a south-facing roof, a lot of glass can add heat faster than a rooflight can lose it, and the right answer is to cut the heat at the glass as well as venting it. That is the job of solar control glazing, which is covered in solar control glass for south-facing rooflights. Blinds on the inside help a little, and blinds fitted outside the glass help more. A good scheme uses both: glass that limits heat, and a vent at the top for what gets through.
Ventilation also works against heat loss in winter if it is left open, so the habit is to open it for a short, wide purge and then close it. Short and wide beats long and narrow in both seasons. A quick burst of fresh air also changes the room faster than a gap left open for hours, because the walls and furniture stay warm while the stale air goes out.
Next steps
Opening rooflights sit within the range described on electric opening rooflights, and manual versions are available across roof windows and flat-roof skylights. Our work is the installation: the opening, the frame, the weathering, the finish inside, and the Building Control notification where the work is notifiable. It carries our 10-year workmanship guarantee.
The best way to get the ventilation right is to look at the room. Book the free survey and we will see where the heat collects, where the replacement air will come from and which type of unit suits the roof. You then receive a fixed written quote. You can also send a photo of the room on WhatsApp.