The super-rich already do this in London[1]. Though there is legislation in the works to limit maximum depth as well as height[2]. 1 - http://www.theguardian.

The super-rich already do this in London[1]. Though there is legislation in the works to limit maximum depth as well as height[2]. 1 - http://www.theguardian.com/artanddesign/2012/nov/09/billionaires-basements-london-houses-architecture http://www.theguardian.com/artanddesign/2012/nov/09/billiona... 2 - http://www.wsj.com/articles/SB10001424127887323893504578559523601890986 http://www.wsj.com/articles/SB100014241278873238935045785595...