Will all houses facing south be sultry in summer? For those who have lived.

Not bad, actually. It depends on your choice. It would be better if it wasn't the top floor. I live in the south now. It's particularly warm in winter and acceptable in summer, but it's certainly not as cold as the room in the north. Opening the small window of the security door can play the role of small convection, and you can also install the old push-pull security door, which has the best convection effect. If the stairs have windows, it is equivalent to the effect of north-south convection!