> that place was 38°C in my living room with all windows and doors open in the summer. If your window is open you will have the same air temperature as outside

> that place was 38°C in my living room with all windows and doors open in the summer. If your window is open you will have the same air temperature as outside, potentially higher. I saw a lot of that in my apartment block this summer. People don't have experience dealing with high temperatures, and intuitions they have are wrong. What you want to do is 1. Open windows at night to create draft and cool down your dwelling. 2. During the day close windows and block sunlight as much as possible. Blocking sunlight on the outside of window is better than blocking it inside. If blocking inside with something like thermal curtains you may need to leave window a crack open. Sunhouse-like conditions may cause temperature next to window increse by a lot (60+) which is not good for glass. 3. (1) and (2) can be supplemented with AirCon, but it's not that popular in UK.