[ItsMe000001]

I live in one such building. It takes one week of high temperatures and it remains hot inside no matter the temperatures, it takes a week of cool weather. That has nothing to do with the topic though, and 15 °C at night is not a heat wave no matter how bad the design.

By the way, I found by personal experiment that all it takes is one layer of something like cloth in front of the stone to prevent if from heating up. I completely cover my large balcony on the outside now, including the thick stones. In all previous years they always stored to much heat during the day that the balcony remained hot well until morning, heat radiating from all sides, making it almost unbearable to go there (or to open the wide door) even when the outside air temperatures had dropped below 20 °C. The difference this summer is huge. So it does not take anything fancy or expensive at all, just prevent direct sun exposure of those heat sink surfaces (like solid concrete).