Introduction
Green roofs have been developed since ancient time when people paid more attention to landscape value of green roofs, and the ancient “Hanging Gardens of Babylon” is a famous case in point. However, benefits of green roofs are far more than that. With the rapid urbanization, city tends to be high plot ratio, high density and high rise while green space shrinks, environment and energy problems become more urgent than before. And green roofs are considered as one of the effective ways to deal with these challenges and improve city image. More and more areas have issued incentive policies to promote the development of green roofs.