The Treasury, Athens, Greece
In 2008, the Greek Ministry of Finance installed a green roof atop the Treasury called an oikostegi. A 2009 study by the Metsovio National Technical University revealed that air-conditioning costs for the building had been reduced as much as 50 percent in the floor directly below the rooftop, and as much as 9 percent throughout the 10-story, 130,000-square-foot building. Further, researchers noticed that an abundance of insects had moved onto the rooftop, including honeybees, ladybirds and butterflies. Oikosteges Director of Environmental Science Vanya Veras says, "The Oikosteges green roof system not only sustains plant growth in the harsh and diverse Mediterranean climate, it enables the development of an ecosystem over the first two years with only three cubic metres of water per 100 square meter [about 106 cubic feet per 1,100 square feet]. Once established, this ecosystem needs no further intervention or watering to survive. In view of the increasing scarcity of drinking water, this aspect of the Oikostegi is essential."