When daylight cannot easily reach a room through its walls — because the space is deep in the plan, on the top floor, or surrounded by other buildings — the answer is often to bring light in through the roof. A skylight is a window set into the roof or ceiling that admits daylight from above. Good skylight design can transform a dark interior, filling it with even, generous natural light that no wall window could deliver. But the roof is also the part of a building most exposed to sun, rain and heat, so a skylight must be designed carefully to avoid leaks and overheating.
This article explains what skylights are, how they bring light into a building, the main types, the benefits they offer, and the practical risks — heat gain, glare and water — that have to be managed for a skylight to perform well.
What a skylight is
A skylight is a glazed opening in the roof that lets daylight enter from overhead. It can be a simple fixed pane, a ventilating unit that opens, a domed rooflight, a long glazed strip or a large structural glass roof over an atrium. What unites them is the direction of light: a skylight lights a space from above rather than from the side.
Light from overhead has a particular quality and value. Because it comes from the brightest part of the sky and falls directly into the room, a skylight can deliver far more daylight per unit area than a vertical window, and it lights the centre of a room rather than just the perimeter. This makes skylights especially useful for top-floor rooms, deep-plan spaces, stairwells, corridors and rooms with no available external wall.
How skylights bring daylight in
A horizontal or sloping skylight sees a large portion of the sky and receives daylight throughout the day, so it is one of the most efficient ways to admit natural light. This makes skylights a powerful tool for good daylighting, reducing the need for artificial lighting in the centre of a building.
Designers shape the way a skylight delivers light in several ways:
- Direct skylights let light fall straight in, giving bright, sometimes intense illumination and, depending on orientation, patches of direct sun that move across the room.
- Light wells and splayed reveals channel light from a roof opening down through a ceiling void into the room below, spreading and softening it.
- North-facing roof glazing (in tropical and northern-hemisphere settings) captures bright but diffuse daylight while avoiding the harsh direct sun and heat of other orientations — the principle behind the sawtooth rooflights of traditional factories and studios.
- Diffusing glazing scatters incoming light to reduce glare and even out the illumination.
Some skylights also serve ventilation: an opening rooflight lets hot air escape from the top of a space, supporting natural ventilation through the stack effect, much as a high clerestory window does.
Types of skylight
Skylights come in several common forms:
- Fixed skylights: sealed glazed units that admit light but do not open; simple and weathertight.
- Ventilating skylights: units that open, by hand or motor, to release warm air and provide ventilation.
- Domed rooflights: curved, often plastic, units common on flat roofs, shedding water easily.
- Tubular skylights (sun tunnels): a small roof dome connected to a reflective tube that carries daylight down into a room below, useful for small or deep spaces.
- Glazed roofs and lanterns: larger structural assemblies, including the great glass roofs over atria and the raised glazed lanterns over halls and stairs.
The right type depends on the roof, the space below, the climate and the balance wanted between light, ventilation and weather protection.
Benefits of skylights
Well-designed skylights deliver real value: abundant, even daylight that lifts the quality of a space and reduces lighting energy; light brought to places that walls cannot reach; a connection to the sky and the changing weather that improves the experience of a room; and, with ventilating units, a route for warm air to escape. In top-lit spaces, the daylight is often more even and pleasant than side light, with fewer dark corners.
These benefits make skylights a recurring feature in homes, studios, galleries, schools, shopping centres and workplaces — anywhere natural light is wanted in the depth of a plan.
The risks: heat, glare and leaks
The roof is the most exposed surface of a building, and a skylight inherits that exposure, so the same opening that brings light can bring problems if it is not designed well.
Heat gain is the first concern. A horizontal or sloping skylight facing the sun can admit a great deal of solar heat, and in a hot, sunny climate an unshaded skylight can cause serious overheating, turning a daylight feature into an air-conditioning burden. The answers are careful orientation, shading, high-performance glazing that admits light while rejecting heat, and sometimes keeping skylight areas modest. Glare from direct sun and bright sky also has to be controlled, often with diffusing glazing or shading.
Water ingress is the other major risk, and it is unforgiving. A skylight is a hole in the roof, the part of the building that must keep out rain, so the junction between the skylight and the roof — the flashing and weatherproofing — must be detailed and built correctly. Poorly installed skylights are a common source of leaks. The glazing itself must also resist wind uplift and, on larger units, carry its own weight safely across the opening.
Because a skylight involves cutting into the roof structure, framing the opening and ensuring loads pass around it, it is partly a structural matter as well as an architectural one — especially for large glazed roofs or when adding a skylight to an existing building. If you are introducing a skylight or a glazed roof and need the opening and structure verified, our structural-engineering consultancy can advise, and you can get in touch to discuss a specific project.
Frequently asked questions
What is a skylight?
A skylight is a glazed opening set into a roof or ceiling that admits daylight from above, lighting a space from overhead rather than from the side and bringing natural light to rooms that walls cannot easily reach.
Why do skylights provide so much light?
A skylight faces a large portion of the bright sky and receives daylight throughout the day, so it admits far more daylight per unit area than a vertical window and lights the centre of a room rather than just its perimeter.
What are the main types of skylight?
Common types include fixed skylights, ventilating skylights that open, domed rooflights for flat roofs, tubular sun tunnels that carry light through a reflective tube, and larger glazed roofs and lanterns over halls, stairs and atria.
Do skylights cause overheating?
They can; a skylight facing the sun admits both light and heat, and in hot, sunny climates an unshaded skylight can cause serious overheating, so good design uses careful orientation, shading and high-performance glazing that admits light while rejecting heat.
Why do skylights sometimes leak?
A skylight is an opening in the roof, the surface that must keep out rain, so if the flashing and weatherproofing at its junction with the roof are poorly detailed or installed, water can get in; correct detailing and installation are essential to prevent leaks.
Related reading
- Thermal Mass in Building Design Explained
- Daylighting in Architecture: A Practical Guide
- Universal Design in Architecture: The Seven Principles
- Net-Zero Energy Buildings Explained: How They Work
Adding a skylight or glazed roof and need the roof opening and structure checked? Talk to our consultancy or get in touch.
