Living in a large house in the suburbs has a far greater environmental impact than living in an apartment in a city by basically any metric you care to measure.
Doesnt large house take more energy to heat? Don't people in the burbs drive more?
Just google for 'suburbs environmental impact' you'll get thousands of hits/studies
http://www.nbwctp.org/resources/the_environmental_impact_of_...
" if you want to be good to the environment, stay away from it. Move to high-rise apartments surrounded by plenty of concrete. Americans who settle in leafy, low-density suburbs will leave a significantly deeper carbon footprint, it turns out, than Americans who live cheek by jowl in urban towers."