How an old flat handles heat, and why the nights are the problem

The options around summer heat indoors are set out side by side below, with the conditions that genuinely favour one over the other.

Thermal mass, and the delay

Thick masonry walls absorb heat slowly through the day rather than letting it pass straight through, which keeps rooms cool through the morning. That stored heat has to go somewhere, and it radiates inward through the evening and into the night. The result is a lag of several hours between the hottest outdoor moment and the hottest indoor one.

In a hot spell that lasts days, the walls never fully cool overnight and the baseline temperature inside climbs. This is why the third and fourth days of a heatwave are far worse indoors than the first, even at the same outdoor temperature.

Shutters are not decoration

External shutters stop sunlight before it reaches the glass, which is far more effective than any curtain on the inside. Once light passes through a window it becomes heat inside the room, and internal blinds can only re-radiate some of it back. The traditional pattern is to close shutters through the day and open them at night, which contradicts every instinct about light and air.

Put simply, a room kept dark all day and opened at dusk will be dramatically cooler than one left bright and open. This is why old streets look shuttered and lifeless in August afternoons, and it is competence rather than absence.

Moving air through

Opening one window achieves very little, because air needs somewhere to leave as well as somewhere to enter. Opening windows on opposite sides of a flat creates a through draught that exchanges the air in minutes rather than hours.

Flats with windows on only one side, which are common in narrow buildings, cannot do this and stay hot much longer. Internal doors propped open matter as much as the windows, since a closed door stops the path entirely. A fan positioned to push hot air out of a window works better than one pointed at a person, though both have their uses.

The night routine

The workable pattern is to open everything once the outside temperature drops below the inside temperature, which may be late. Checking rather than assuming is worth it, because opening windows while it is still hotter outside makes the flat worse. Closing everything again before the sun reaches the windows in the morning locks in the cool air you gained.

For most people, top-floor flats under an uninsulated roof are a different problem entirely, since the roof radiates heat downward all night.

Anyone choosing a flat for summer should weigh the top floor view against what August will be like up there.

Cooling that is not air conditioning

Air conditioning is far from universal in older buildings, partly because installing units is restricted on protected facades. Fans, shutters, ventilation and behaviour do most of the work in most homes, and they are more effective than people expect. Damp cloths, cool showers and keeping the body cool rather than the room is the traditional approach and is genuinely sensible.

Cooking heats a flat substantially, which is one reason eating out or eating cold food in summer is a habit rather than a treat. Portable units exist but need an exhaust hose out of a window, which shutters and casement windows make awkward.

None of this is a substitute for talking to a clinician if something feels wrong.

Who is actually at risk

Sustained indoor heat is a health issue rather than a comfort issue for older people, infants and anyone with a chronic condition. Night-time temperatures matter most, because the body relies on cooler nights to recover from daytime heat.

On an ordinary week, checking on older neighbours during a hot spell is a small act that matters, and it is a normal part of building life here. Anyone feeling unwell in heat should cool down, take fluids and seek medical help rather than waiting to see. This is general information; anyone with a health condition affected by heat should discuss it with a qualified professional.

Side by side

The takeaway

Shut it up by day, open it at night, and get air moving through, not into.

Pick the one that costs you least, and let the rest wait.