My personal dream is house built into a slope. So earth around half-ish of the house can be used as thermal mass all year round. Currently roof becomes heated.

My personal dream is house built into a slope. So earth around half-ish of the house can be used as thermal mass all year round. Currently roof becomes heated. And there's crapton of insulation in the attic. Which heats up during the day in sunlight.. And then takes it's sweet time to cool down at night. And, if heat lasts several days, it doesn't even cool down by the morning. Another solution would be a full-sized attic like in old houses. Now we didn't even bother to install crawl doors, because there's next-to-no space. Insulation takes up whatever is there. But large attic would be inefficient in winter. Unless we'd double-insulate it to keep heat in living quarters. But I wonder how long it'd take to recoup €€€€ and kwh/co2/etc spent for extra building materials/work wit lower energy usage.