Green roofs can provide several benefits, not only to the building itself but also to the city environment. Besides the mitigation of noise pollution or the moderation of temperatures inside buildings, vegetated roofs also help to filter and purify the air and offset overheating generated by the city. In addition, having a permeable surfaces minimises the effects of floods and lessens the possibility of leaks. Being really as beneficial as they look the remaining question is: why aren’t we turning every unused and cemented rooftop into green spaces? Well, Copenhagen, San Francisco and Paris have already started!

Starting at a city scale…

By 2009 Denmark was in charge of the UN Climate Change Conference COP15. During that period the focus on green roofs intensified and the city ended up setting a goal for urban design with green roofs in the Climate Plan of the City of Copenhagen. The mandate of green roofs for all Municipalities buildings was one of the guidelines. But today Copenhagen has more than 40 green roofs installed on a number of different types of buildings from residential condominiums to libraries to cruise terminals.
Also in 2009, Toronto City Council adopted a bylaw requiring and governing the construction of green roofs on new developments. This was first applied to new building permit applications for residential, commercial and institutional development but then extended to industrial buildings in 2012.
This year, 2016, San Francisco became the first city in USA where it is required that new buildings incorporate from 15 to 30 percent of roof space with solar or green roofs

and extending to the whole country…

Curiously, in the year that Paris hosted the COP21, France tried to approve a project law stipulating that any new building in a commercial area would have to install vegetation devices or renewable energy production on all or part of the roof. Although the approval of the law was widespread in 2015, the law for the biodiversity act and green roof statement has been slowed down by the Senate, which claimed lack of study on the negative impact of green roofs. But it seems now it is official and by 2017 “Bringing nature back into the city” with an“obligation for every new commercial development to integrate green roofs OR solar panels”. Some problems might come from this “or” as many developers might be more likely to choose solar, but it’s undeniable that this is a major step in the right direction. In turn Paris is taking this direction seriously as the Mayor Anne Hidalgo stipulated the goal of creating 100 hectares of living walls and green roofs by the year 2020.