Or just more living / working space. Say you're in one of many low to medium density areas (sf, suburbs of nyc, etc) and need more living space. Going up is v

Or just more living / working space. Say you're in one of many low to medium density areas (sf, suburbs of nyc, etc) and need more living space. Going up is very expensive and causes conflicts with the neighbors (earthquake zone, views); down is even more expensive; building in the yard loses, well, the yard. So going under the yard is not a crazy option. Particularly in our brave new wfh world where employees now have to pay for their own working space.