Clerestory Windows Explained

A row of windows placed high up in a wall, above eye level and often above the roofline of an adjoining lower space, is called a clerestory. Clerestory windows let daylight pour into the upper part of a room and reach deep into the interior, far further than ordinary windows at eye level can. They are one of the oldest and most reliable ways to bring natural light into the centre of a building, used everywhere from ancient temples and Gothic cathedrals to modern offices, factories and homes.

This article explains what clerestory windows are, how they work to light a space, where the idea came from, the different ways they are used, and the practical issues — heat, glare and structure — that come with putting windows high in a wall.

What clerestory windows are

A clerestory (pronounced “clear-story”) is the upper part of a wall that rises above adjacent roofs and contains a band of windows. The term originally described the high windowed level of a church nave, lifted above the lower aisle roofs so light could enter from above. By extension, any high-level window that brings light in above eye level is now called a clerestory window.

The defining feature is height. Because the window sits high in the wall, the light it admits falls onto the ceiling and the back of the room rather than just the area near the glass. High windows light a room more evenly and more deeply than low ones, which is the whole point of the clerestory.

How clerestory windows work

Daylight entering a window penetrates a room roughly in proportion to the height of the window head above the floor. A window placed low lights only the zone near it; a window placed high throws light much further in. This simple geometric fact is why clerestory windows are so effective at daylighting deep interiors.

Clerestory windows deliver several advantages at once:

Deep daylight. Light from high windows reaches the centre and back of a space, reducing the need for artificial lighting away from the perimeter.
Even, diffuse light. Because the light often arrives via the ceiling, it spreads more evenly and with less harsh contrast than direct low-level sun.
Privacy with light. A high window admits daylight without giving a view in or out at eye level, useful where privacy or wall space for furniture and display is needed.
Ventilation. Opening clerestory windows lets warm air escape from the top of a room, driving natural ventilation through the stack effect, since hot air rises and exits high up.

That last point links the clerestory to passive cooling: high-level openings release the hottest air, drawing cooler air in lower down — a particularly valuable strategy in warm climates.

Origins: temples and cathedrals

The clerestory is ancient. Egyptian temples used high openings to admit shafts of light into otherwise dark halls. Roman basilicas raised the central nave above the side aisles and pierced the upper wall with windows, lighting the great interior spaces from above.

The clerestory reached its most spectacular development in the medieval church, and above all in Gothic architecture. The Gothic cathedral is, in section, a tall central nave flanked by lower aisles, with a high clerestory level of large windows above the aisle roofs. As Gothic structural techniques — the rib vault, the pointed arch and the flying buttress — moved the building’s loads onto slender piers and external buttresses, the clerestory walls could be opened into enormous expanses of stained glass. The flood of coloured light from high above was the spiritual and architectural climax of the cathedral, and it was made possible by the clerestory.

Clerestory windows in modern architecture

The clerestory never went away, because the problem it solves — lighting the depth of a building naturally — is universal. Modern architects use clerestory windows in many ways:

In houses, a band of high windows brings daylight into living spaces while keeping wall space and privacy below.
In offices and schools, clerestories light deep floorplates and bring daylight past the perimeter, reducing reliance on artificial light.
In factories and warehouses, high windows or roof clerestories (sometimes in a sawtooth roof profile) flood large floor areas with even daylight.
In places of worship and civic buildings, clerestories continue to provide the dramatic, elevated light that has defined such spaces for centuries.

The mid-twentieth-century modernists, with their interest in light, openness and connection to nature, used clerestory bands extensively, often as a strip of glazing where wall meets roof, dematerialising the junction and letting the roof appear to float on light.

Practical considerations: heat, glare and structure

Clerestory windows admit light, but light brings heat, and high windows facing the sun can cause overheating and glare. In a hot, sunny climate this matters greatly: an unshaded clerestory can turn a daylight feature into a source of unwanted solar gain. The usual answers are careful orientation (north-facing clerestories in the tropics catch less direct sun), external shading or louvers, and appropriate glazing. The aim is to keep the daylight while controlling the heat.

Structurally, raising part of a roof to create a clerestory means the wall above must be supported and the change in roof level detailed for weather, movement and wind. On larger buildings the band of high glazing interrupts the wall and must be framed so loads pass around it cleanly. These are routine but important matters that need to be settled in design. If you are introducing clerestory glazing — particularly when cutting into an existing roof or wall — our structural-engineering consultancy can confirm the structure works.

Frequently asked questions

What are clerestory windows?

Clerestory windows are a band of windows set high in a wall, above eye level and often above an adjoining lower roof, that bring daylight into the upper part of a room and let it reach deep into the interior.

Why are clerestory windows placed high up?

The higher a window’s head, the further its light penetrates into a room, so placing windows high lets daylight reach the centre and back of a space, light it more evenly, and provide light without a view in or out at eye level.

Where did clerestory windows originate?

Clerestory windows go back to ancient Egyptian temples and Roman basilicas and reached their fullest development in medieval Gothic cathedrals, whose high nave windows above the aisle roofs flooded the interior with light through expanses of stained glass.

Do clerestory windows help with ventilation?

Yes; because warm air rises, opening clerestory windows lets the hottest air escape from the top of a room and draws cooler air in lower down, driving natural ventilation through the stack effect, which is valuable in warm climates.

What are the drawbacks of clerestory windows?

High windows facing the sun can cause overheating and glare, so they need careful orientation, external shading or louvers and suitable glazing; raising part of a roof to create them also requires the structure above and around the opening to be properly designed.

Adding clerestory glazing or cutting into an existing roof and need the structure checked? Talk to our consultancy or get in touch.