Spanish homes (specially south & east, plus islands) are mostly prepared for the heat. There's a seesaw pattern:

The older the better: Thicker walls, good orientation, good ventilation with small windows on first floor... It depends on the area); but also newer buildings have efficient insulation and good AC machines.

It's the cheap, built between 70-90s houses that may lack some stuff.

The only reason most of us aren't <more> adapted is that we aren't as rich as northern Europeans.