Courtyard windows versus the street
The cooler intake is usually the greener, shadier, more sheltered side. Street façades hold heat, noise, and often worse air. Use them as exhaust when you can.
Two windows in the same flat can face two different climates.
A courtyard with plants, shade, or a light well is often several degrees cooler in the evening than the street façade of the same building. A street window sits above asphalt that has been storing sun all day. That is the local face of an urban heat island.
Prefer the sheltered side as intake
When you have a choice, pull air from:
- Trees, a park, a planted courtyard
- The façade that stayed in shade through the afternoon
- Water, if you have it and the air is moving
Push air out through:
- The street, the traffic, the sun-baked wall
- The side that was in sun all day
That is the same ranking Ventilate uses when you say what sits outside each window. City and street lean toward exhaust. Garden and trees lean toward intake. A tight courtyard can also go stagnant: open it when it is clearly cooler, not just because it is inside the block.
If you only have the street
Plenty of flats are single-sided onto a road. You cannot invent a courtyard.
- Wait until outdoor air is actually cooler. On a heat-island street that may be later than the forecast for the countryside
- Use a fan on the sill to pull night air in, then mix the room
- Keep daytime shutters down. The street façade is usually the solar load
- If air quality is poor, keep openings short: dirty air versus indoor heat
Noise is a clue, not the rule
A loud street is often also a hot, dirty one. Closing for noise at 2 am can trap the day’s heat. If you must keep a street window mostly shut, crack a smaller opening and run the fan, rather than sealing the only path you have.
Night flush still has to happen somehow: how to flush heat overnight.