The central courtyard: how it draws heat out of the house

"A courtyard in the middle keeps the house cool." It is half true. A well-designed courtyard really does draw heat out, and it does so in four different ways. A badly designed one (wide, paved and in full sun, or roofed over with clear sheeting) does the opposite: it becomes the hottest room in the house and hands that heat to all the others.

This is what a courtyard does with air and with heat, with the physics told without more formulas than needed, with Cali's climate as Colombia's weather service measures it, and with the cases in which it does not work. There are some, and they are worth knowing before you draw one.

First, the climate it has to work in

Cali (a city in a valley in south-western Colombia, roughly 900 to 1,000 metres above sea level) does not have a single climate, not even within its own municipal boundary. Annex 2 of Resolución 0194 de 2025 of the Ministry of Housing (Colombia's current sustainable-building rule, which replaced Resolución 0549 de 2015), in its December 2024 edition, divides Cali's area like this: 50.3% temperate, 28.3% hot and dry, 11.1% cold and 10.2% hot and humid.

To know what a courtyard has to work with, a weather station tells you more than a class. IDEAM, Colombia's institute of hydrology, meteorology and environmental studies, publishes the 1991-2020 climate normals (thirty-year averages) station by station. The one at the Universidad del Valle, in the south of Cali, at 996 metres, reads like this:

Read that table with two ideas in mind. Cali's nights are cool: almost eleven degrees below the afternoon. A house that opens up at night and shuts out the day starts ahead. And the humidity is not that of the Caribbean coast, but it is not low either: water evaporating in a courtyard cools less than a photograph suggests.

What a courtyard does, in four mechanisms

1. It gives every room a second facade

Air does not cross a room that has a single window: it comes in and goes out through the same opening, and the room barely changes its air. To cross, it needs an inlet and an outlet on different sides. In a compact house the rooms in the middle have no facade at all. The courtyard gives them one: each room ends up with a window to the outside and a door or window to the inside, and the air has a way through.

It is the strongest mechanism and the least showy. It depends on the wind: when it blows, the side facing it is under pressure and the opposite side under suction, and the air runs from one to the other. One condition, lost in many renovations: interior walls and doors must not block the way. A room with its window to the courtyard and its door to the corridor always shut is back to a single facade.

2. It stores the cool of the night

At night, everything that sees a clear sky gives off heat to it by radiation: the courtyard floor, the leaves, the roof. The air that touches those surfaces cools, grows heavier and settles at the bottom of the courtyard, like water in a well. The World Health Organization, in its guide to natural ventilation, recommends exactly that for hot climates: semi-open spaces that let the ground radiate to the sky, because they lower the temperature people feel.

The practical consequence is the one that matters most in Cali. If the house is open to the courtyard at night, walls and floors shed the heat of the day. A brick wall cooled in the early hours absorbs heat through the morning instead of giving it back. With more than ten degrees between afternoon and dawn, that mass works for you; it is the same hot-and-dry argument made in the article on the four climates.

3. It acts as a chimney, but a weak one

This is the mechanism everyone names. Warm air is lighter than cool air and rises; if there is an outlet high up and an inlet low down, it leaves at the top and is replaced by air coming in at the bottom. That is the stack effect, and it is real. What almost nobody says is what its strength depends on: the height between inlet and outlet, and the temperature difference between inside and out. The WHO formula makes it directly proportional: twice the height, twice the push; twice the temperature difference, twice the push.

Now the sum for a single-storey house. The useful height is that of a room, about three metres. With one degree of difference between the courtyard air and the outside air, the push is one tenth of a pascal. A gentle breeze of one metre per second pushes about five times harder. In other words: in a single-storey house the courtyard is not a chimney; the wind does the work, through mechanism number one. The chimney starts to count when there is height: two storeys, a staircase, a void. That is in the staircase as a chimney.

4. It puts shade, water and leaves where the air is

A tree in the courtyard does two things: it shades the floor, which does not heat up in the shade, and it transpires through its leaves. Water does one: it evaporates, and to evaporate it takes heat from the air. Resolución 0194 describes this as evaporative cooling. Its limit is humidity: the more humid the air, the less water it can take up and the less it cools. In Cali, with mean humidity near 71%, it works, but less than in a dry climate, and less still in April and May, the most humid months in the table.

When a courtyard heats instead of cooling

• —Wide, shallow and in the sun. A concrete or tiled floor in the midday sun stores heat and gives it back in the afternoon and at night, just when you want to ventilate. A courtyard taller than it is wide shades itself for much of the day, but Cali is so close to the equator that the midday sun falls almost vertically and reaches the bottom of any courtyard: a tree, eaves or an awning are never superfluous. No rule sets the proportion: it is a design judgement, made with a section drawing and the path of the sun.
• —Roofed over with clear sheeting, polycarbonate or glass. Sunlight passes through the roof, heats the floor and walls, and the heat they give back can no longer escape. It is a greenhouse. If the courtyard must be kept out of the rain, the roof needs a high air outlet all round, or must be opaque and ventilated, or movable.
• —With no openings connecting it to the house. A courtyard that no opening window looks onto is a garden to look at. It ventilates nothing.
• —Wide open at three in the afternoon. With a mean maximum of 30.1 °C at the Universidad del Valle station, ventilating at that hour lets heat in. The rule itself says so, and we quote it below.

In practice that becomes a timetable: by day, shade and controlled openings; by night, the house open to the courtyard. Shutters, screens and barred doors that can be left open at night without worry are part of the courtyard's design, not an accessory.

What a courtyard costs, and not in money

Rain. The Universidad del Valle station averages almost 1,460 millimetres a year, and April goes past 190. All of it falls inside the house. The courtyard needs falls, properly sized drains, a covered walkway or eaves so people can move around without getting wet, and walls protected at the base. Water splashing against a wall for years ends up as damp rising through the wall, and leaves in the gutters as leaks.

Security. An inner courtyard does not face the street, and that is an advantage. But if the roofs around it can be reached from the house next door, it is a way in. The answer is a horizontal grille or mesh that lets air through, and it is designed in, not added afterwards.

Noise and privacy. Around a courtyard, what is said in one room is heard in the room opposite. It is worth deciding which rooms face each other.

Area. A courtyard uses up plot. Whether it counts towards the site-coverage ratio is set by each municipality's planning rules, and we do not state it here: it is checked against the rules for your plot, as explained in what can I build on my plot. On a narrow urban plot, a small courtyard, a light and air well, does mechanism one on a smaller scale, though not the other three.

How we approach it at the studio

Two of the studio's proposals in Jamundí, the town next to Cali, turn on this idea. In Casa Aguilar, a 2018 proposal to transform an existing country house, the heart of the project is the garden courtyard, and all the main spaces open onto it. In Casa Castrillón, from the same year, the single-storey house is organised around a central garden so that every room gets cross-ventilation.

Five questions before drawing the courtyard

1. 1Does every room have two facades? One to the courtyard and another elsewhere. If not, the courtyard brings light but not air.
2. 2What shades the courtyard floor at midday and at three in the afternoon? A tree, eaves, an awning or the height of the walls themselves. If the answer is "nothing", the courtyard is a radiator.
3. 3Where does the warm air get out? Above the courtyard, through a ridge, through a high window. With no outlet there is no chimney, however weak.
4. 4Where does the April downpour go? Falls, drains and a walkway to move around. It is drawn before the floor.
5. 5What closes at three in the afternoon and what opens at nine at night? If the house cannot be left open at night safely, the courtyard loses half of what it does.

A courtyard is not added at the end: it is decided together with the orientation, the roof and the openings, at the design-concept stage. The comparison of roofs, the other half of a house's heat, is in roofs: clay, insulated metal panel, green or concrete.