Through-breeze window placement

A room cools with a breeze only when air comes in one wall and leaves through the opposite wall of that same room. Two windows on one wall, or a single open door, do not do this.

Why a single opening is not enough

When wind hits a house, it pushes on one side and pulls on the other. An opening on the wind side lets air in. An opening on the far side lets that air out, and takes heat with it. If there is only one opening, air has to enter and leave through the same hole.

The layout

Place the two openings like this:

• In the room people sit or sleep in. An opening in the sitting room and another in a closed bedroom does not cool either room.
• On opposite walls — not on neighbouring walls, and not both on one wall.
• So they can see each other. A partition, wardrobe, or curtain in the line stops the air.
• The wall the wind hits is the way in. The wall opposite is the way out. Feel this at the hot time of day; do not guess from a compass.
• A door counts as one opening if it can stay open. Open eaves leak air, but they are not the hole on the far wall.

How big and how high

The smaller of the two openings sets how much air can pass. Keep them a similar size. A door facing a slit is still almost one opening.

The openings do not need to be huge. Two you will leave open beat one large window you lock.

To cool people, put them at the height of sitting and standing, on opposite walls, at a similar height, so the breeze crosses the room instead of running along the roof.

A lower way in and a higher way out also lets hot air rise and leave. That helps. Openings only up at the eaves take heat out of the roof space but can miss the people below.

If a low window will be shut every night, a smaller one higher that stays open is the better height.

Find the walls on your house

1. Stand outside at the hottest time of day. The wall the wind hits is the way in.
2. In the room you care about, the way out is the wall opposite that one.
3. Look along the line between the two openings. If a cupboard or curtain sits there, move it, or the air stops.
4. If you have only one opening, the second belongs on the opposite wall of that room — not beside the first, and not around the corner.
5. If the house is several rooms, put both openings in one room, or leave the inner door on that path open.
6. On a windy afternoon, hold steam or smoke at the wind-wall opening. It should leave through the far opening. If it dies in the room, the path is blocked or the second opening is on the wrong wall.

Layouts that fail

• One opening only.
• Two openings on the same wall.
• The two openings in different closed rooms.
• A wardrobe, curtain, or shut inner door on the line between them.
• The far wall faces a blocked alley with no sky. That wall cannot dump air.
• A door facing a hole the size of a brick.
• Both openings only at the roof, with people sitting in still air below.

When this does not apply

In still air there is nothing to pull through. On a cold highland night you will close the openings, and the layout does nothing. In a flat or packed plot with only one wall to the open, you cannot place an opposite outlet. Do not force it.

Sources

• Ochomo, Maggioni and colleagues, housing modifications in rural western Kenya, Nature Medicine (most study houses had few or no windows; a through-path is not how those houses were built).
• Li and colleagues, traditional houses around Kisumu: air often enters at eaves and a door, not through opposite windows.