London is seeing a bit of this - people are building massive 3+ story basements under existing properties. http://www.cnn.com/2014/01/24/business/going-underground-lon...
For anyone interested, there are a few Grand Designs episodes featuring underground residential work. Some are quite inventive due to space constraints. Amazing how expensive some of the groundworks can be dealing with weather or underpinning neighbouring properties.
In my city that's where they put parking spots which are even more profitable than housing per square foot. Over $60k a spot.
I have a naïve question about subterrean _housing_.
With the real estate skyrocketing in some cities, and scarcity of terrain, I wonder why there is not much more underground liveable habitations (for example, near an expensive city center with no space left).