This Incredible Tool (preventing insolation) That Our Ancestors Used To Keep Cool In The Summer.
Yeah, they cost money. So does installing air-conditioning. But they use no energy ( that’d would be bad for fossil energy-producers).
So, I’m lucky enough to have built a house, and earthworks are expensive. A hobbit hole would cost as much as the house we live in, without the actual building, just the hole.
I live in a garden level apartment (I think, it’s mostly underground with one exterior wall above ground for windows, set into a hill) and it’s extremely energy efficient. We do have to use dehydrators, but that can be done in very energy-efficient ways.
The apartments above us are significantly less energy efficient, so the big drawback I see is around housing density, which is probably a bigger issue than heating/cooling energy, but I don’t actually know.
Horses for courses. Every area is different. Some places have geothermal but also need constant heating, so a geothermal town heating system with high density makes sense. Other places are near the equator, and actually need to sink as much heat as possible year round, so separate housing with a lot of greenery to keep everything cool works better. In other places heat and cold is mild so good passive thermal design works well.
Where I live for example, it’s good to prioritise air flow and thermal management, something which is significantly harder in an apartment. Having said that, during particularly cold nights, an apartment actually works better (but this is for a month in the year).