Volcanic insulation on Gran Canaria

The southern end of Gran Canaria is very arid. They have put in a lot of tourist apartments by the sea. The flat roofs seem to be covered in the local volcanic rock. I assume that this is insulation to maintain a cooler temperature inside, which is the opposite of what we need up north in the winter. The rock is porous due to gas bubbles in the lava flows and thus it traps air. This makes it a poorer conductor of thermal energy thus causing it to take longer for the thermal energy to get through into the house.