> Up until as late as 1989 you could get a tax credit if you included one in your homes build. Some even got straight up subsidized.

With climate change, building underground may still have a financial benefit even without a tax credit or subsidies. It'll cost more to build, but operational costs would be lower if build properly.

You don't have to go that deep to get fairly consistent year round temperatures. Where I'm at, a horizontal geothermal HVAC loop gets installed around 6-8 feet deep and stays at about 50-55°F degrees year round.

Then again, with walls 3 meters (10 feet) thick, it's already got a fairly heafty thermal mass to moderate temperatures even if it was entirely above ground.

I have a propane fire pit on our porch that takes forever to heat the thermocouple using just the regular flame from the burner. I also do the mapp gas torch trick to speed up the process.