It has been a controversial question in the home real estate market for years: Is there extra green when you buy green? Do houses with lots of energy-saving and sustainability features sell for more than houses without them? If so, by how much?

Some studies have shown that consumers’ willingness to pay more for Energy Star and other green-rated homes tends to diminish during tough economic times. Others have found that green-certified houses sell for at least a modest premium over similar but less-efficient homes.

But now a new study involving an unusually large sample of 1.6 million homes sold in California between 2007 and early 2012 has documented that, holding all other variables constant, a green certification label on a house adds an average of 9 percent to its selling value. READ MORE …