Stand in a dark kitchen with a builder and a roof overhead, and the word skylight stops being useful. It can mean a window in a sloping loft ceiling, a glass panel in a flat extension roof, a pitched glass crown over a dining table or a small dome that sends light down a tube. Those are different products, built to different standards, fitted by different methods, and they cannot be swapped for one another once the roof is made.
Trade names add to the confusion. In this guide a skylight is the everyday word for any glazed opening in a roof, and rooflight is the term we use for glazing on a flat or low-pitched roof. The seven sections follow the choices in the order most people meet them: first by shape of roof, then by how the glass behaves, then by where it will be seen. A table at the close pairs each type with its roof. Wherever a choice affects the builder, we say what goes in writing before the roof is made.
Roof windows
A roof window is a window made for a sloping roof. It sits in the same plane as the tiles or slates, in a frame that is flashed into the covering so rain runs over and around it. It is the right answer for a loft bedroom, a landing, a study under the eaves or any pitched slope where the glass should look like part of the roof.
There are two usual ways a roof window opens. A centre-pivot unit turns on a bar halfway up the sash, so the top swings outward and the bottom swings in. It gives a good view out when you are standing and can be rotated for cleaning the outside pane. A top-hung unit hinges at the top and opens outward like a canopy, giving more headroom under the sash and a larger clear opening, which matters where the window must also serve as a way out.
Size is quoted in manufacturer codes. For VELUX units the letter is the width and the digits the height, so the code tells you the frame before you reach the brochure. The flashing kit, which adapts the frame to the roof covering, is chosen to suit slate, plain tile or profiled tile, and it is part of the quote. More on this family, including loft use, is on our roof windows page.
Because a roof window cuts the rafters, the opening has to be trimmed, and in most homes the work is notifiable. Our guide to Building Regulations for rooflights sets out what the inspector will look at.
Flat rooflights
A flat rooflight is a pane or panes of glass in a frame, set on a low upstand over an opening in a flat or very shallow roof. It gives a single clean slab of daylight, and it is the standard choice on a single-storey rear extension, a kitchen or utility behind a parapet, a garage conversion or a side-return roof.
The glass is sealed double or triple glazing, usually with a laminated inner pane. The frame can be a slim profile that sits on the kerb with almost no visible edge, or a thicker trim with a visible frame on the inside. Some are fixed, and some include an opening section, covered below.
A flat roof is laid to a slight fall so water runs away, and the kerb under the glass lifts the unit above where that water travels. Without an upstand the glass would sit level with the membrane, where water could stand against it. The maker states the upstand height for each unit, and the builder works to that figure.
Where the roof is covered with EPDM, GRP or felt, the roofer takes the covering up the kerb first, and the glass is fitted once the roof is watertight. That sequence is the reason the kerb size has to be on the builder's desk before the deck goes on. Our note on who builds the kerb covers the usual split of work. For the family overall, see flat roof rooflights.
Roof lanterns
A roof lantern is a raised glazed structure on a flat roof, usually with a pitched or hipped glass crown and a ridge. Where a flat rooflight is a pane in the roof, a lantern is a small glass roof above it. It takes light from several angles, which gives the room below a different quality of light across the day, and it adds height that you can see from inside and out.
Lanterns are typically built from aluminium or, in some ranges, uPVC, with glazing bars that hold the panes at a slope. They sit on a kerb like a flat rooflight but are heavier and taller, so the structure under them has to be designed for the extra weight. Their shape comes in a few families: a hipped lantern with sloping ends, a pyramid or square lantern for a square room, and a gable-ended lantern with vertical end walls.
On a modern extension with a high ceiling, a lantern gives drama in the middle of the room and makes a large flat roof feel less heavy. The trade-off is height outside. A lantern stands above the roof line, which matters for neighbours, for the view from upstairs windows, and, in some places, for planning. Our separate pages on choosing between a lantern and a flat rooflight and on lantern sizes and kerb dimensions go through those decisions in detail.
Lanterns are made to measure, and the stated size drives the lead time. The maker names it and our quote repeats it, so the glass is ordered to arrive as the roof becomes ready, not before and not after. The full range is on our roof lanterns page.
Opening and electric units
Opening is a feature rather than a separate shape. Roof windows, flat rooflights and lanterns can all be made with a section that opens. What changes is how it is operated. A manual unit has a pole, a handle or a lever. An electric unit has a motor, called an actuator, that lifts the glass at the touch of a switch, a remote or a wall panel.
The case for opening is ventilation. Warm air rises, and a section that opens in the roof lets it escape, which helps in a kitchen over the hob, on a hot afternoon in a glazed extension or in a bathroom. An opening section lets warm, moist air leave a room, though it does not stop condensation and it does not replace an extract fan where one is needed. Electric roof windows can also carry a rain sensor that closes the sash when drops fall.
Reach matters. A manual opening unit works only where you can get to it. High rooflights over double-height spaces, over a stair or above fixed furniture are usually specified as electric. A switch by the garden doors, as in a kitchen extension, also keeps the room tidy.
Wiring is the part to plan. The cable for the motor is run at first fix, while ceilings are open, and it ends at a switch or control point chosen with the electrician. If it is left until after plastering, the route is chased out of finished walls. A mains-powered unit and a solar-powered one differ here: solar units avoid the cable but depend on light at the roof. We cover the options on our electric opening rooflights page, and the sequence is one reason we speak to the electrician as well as the builder.
Walk-on and conservation units
Two families stand apart from the rest because they answer a particular problem. Walk-on rooflights take the weight of people. Conservation rooflights fit into old roofs without changing how they look.
A walk-on rooflight is structural glass set flush into a floor, a terrace or a patio, with light dropping through to the room below. The glass is multi-layer and laminated, with an anti-slip surface, and it is designed for a stated load, which is given by the maker. It works for a basement kitchen under a garden, a terrace deck above a living room or a path across a lightwell. The frame and the structure below are designed together, so the drawings matter more than for any other type. Our walk-on rooflights page describes where they suit.
A conservation rooflight is a slim, cast-metal-style unit made to sit low in the roof, usually with a centre glazing bar and a thin frame that mimics the older cast iron lights found in Victorian roofs and farm buildings. It sits close to the slate or tile, and it is the type chosen for listed buildings, conservation areas and National Park land, where a standard roof window would look out of place.
Whether the council will accept it is a planning matter, and the position depends on the address. Permitted development is removed on listed buildings and can be withdrawn elsewhere, so we look up your address, tell you what the position is, and the council has the last word. The rules are in our planning guide, and our conservation rooflights page shows the kind of unit we mean.
Sun tunnels
The sun tunnel is the most compact daylight source of all. A clear dome on the roof catches light, a reflective tube carries it through the roof space, and a diffuser in the ceiling spreads it into the room like a light fitting. The tube can bend round obstacles in the roof space.
It earns its place where a normal window is impossible. A hallway with no outside wall, a landing, a cloakroom, a walk-in wardrobe or an internal bathroom are the typical rooms. The opening in the roof is small, so the structural work is light, and the tube can be rigid for a straight run or flexible for a path with bends.
The limits are clear. A sun tunnel is a source of light, not a view, and it does not open to ventilate. It gives less light than a roof window of the same width and is best compared with a light fitting rather than a window. On a flat roof the dome sits on a short kerb, and on a tiled roof a flashing kit seats it into the covering.
Because a sun tunnel needs only a small opening, it can be added after the roof covering is complete. The choice between rigid and flexible tubing is set by the route through the roof space. See our sun tunnels page for how they are fitted, and the comparison with a roof window in sun tunnel or skylight.
Matching the type to the roof
The roof narrows the field before taste comes into it. A pitched roof takes a roof window, a conservation unit or a sun tunnel. A flat or near-flat roof takes a flat rooflight, a lantern, a walk-on panel or a sun tunnel dome. Settle what the roof allows, and then choose between those.
| Type | Roof it suits | Rooms it serves best |
|---|---|---|
| Roof window | Pitched, tiled or slated | Loft rooms, landings, studies |
| Flat rooflight | Flat or shallow roof | Kitchens, side returns, utility rooms |
| Roof lantern | Flat roof with ceiling height | Dining and living extensions |
| Opening or electric unit | Any of the above | Kitchens, bathrooms, glazed extensions |
| Walk-on unit | Terrace, patio or floor | Basements, rooms under terraces |
| Conservation unit | Old slate or tile roofs | Period lofts, cottages, outbuildings |
| Sun tunnel | Pitched or flat | Halls, landings, cloakrooms |
After the roof comes the build. If a roof is still being made, the unit can be chosen early and its sizes sent to the builder in writing, so the opening or the kerb is built correctly the first time. If the roof exists, the survey records its covering, structure and position, and the written quote lists the unit, glazing and lead time.
Cost follows from all of this, and the answer varies by type and by roof, so we deal with it separately in how much it costs to fit a skylight. If you want a second view before you decide, speak to us about your roof, and we will say which families fit.
Quick questions on choosing
- What is the difference between a skylight and a rooflight?
- Skylight is the everyday word for any glazed opening in a roof. Rooflight is the term usually used for glazing on a flat or low-pitched roof, such as a flat glass panel or a lantern. A roof window is the sloping-roof version.
- Can I fit a lantern where a roof window is now?
- A lantern needs a flat roof and a kerb, so it will not replace a roof window on a pitched slope. The nearest swap on a slope is a larger or paired roof window, set out so the trimming suits both.
