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Someone put up a tent on their balcony to escape their heat-trapping apartment during the night.
(discuss.tchncs.de)
Third extended heat wave within 6 weeks.
The previous one exceeded 40°C, and the buildings not yet had time to completely cool down from that one before the third wave hit.
I was considering putting up a tent in my garden myself, but as I own a ground floor flat, the indoor temperatures did, with the help of some additional cooling measures, thankfully not exceeded 27°C.
You can kinda do some managing of when the shutters are open, half-open or closed as well as when the windows behind them are open or closed, to keep heating from sunlight outside and tilt air-circulation in favor of the colder hours but, yeah, eventually even that is fighting the wall of the building itself having warmed up.
Here in Portugal (were that kind of shutters are also very common) I did manage to, for most days of the one 40C+ heatwave we had, keep the indoor temperature below 30C, though it still creeped up (no doubt due to exactly that effect you mentioned of the building walls heating up) and after some days I actually had to use a fan to help air-circulation with the outside during early-morning and night when the air outside was colder.