Photos: Sizing up Chicago's green high rises

The roof of Chicago City Hall has been covered with greenery since 2001. The project, part of a study with the Environmental Protection Agency, cost $400,000 (£192,000) and has saved the city tens of thousands of dollars in energy bills. The city is offering $285,000 (£137,000) worth of grants to building owners seeking to install green roofs. There are now more than 250 green roofs comprising 93,000 square metres in Chicago.

Credit: Conservation Design Forum