On Thursday, France’s parliament passed a law that requires all new commercial buildings to partially cover their rooftops in solar panels or plants.
French activists originally wanted the law to require all new buildings to sport green rooftops, but the government settled on a measure that applied only to the commercial sector, required only partial coverage and allowed buildings to decide between plants and solar panels. The mandate is similar to Green Roof initiatives around the world, the most ambitious of which is a 2009 Toronto by-law that applies to commercial, industrial, institutional and residential buildings.
Why a building would install solar panels is easy enough to understand, but mandating plant cover requires some explanation. It’s about much more than aesthetic value.
According to Think Progress, green rooftops “significantly reduce the urban ‘heat island’ effect.” This occurs when non-permeable surfaces replace once open land. Take away the greenery; stick in several hundred buildings, roads, sidewalks and other structures; and suddenly there’s a lot fewer things to absorb environmental moisture and heat. The United States Environmental Protection Agency calculates that the “heat island” effect can raise day-time temperatures in large cities by 1.8°F to 5.4°F compared to the surrounding environment, and up to 22°F at night!
Green rooftops help to mitigate this phenomena and offer a range of additional benefits: They reduce the amount of energy needed to heat buildings in winter or cool them in the summer, they retain rainwater and moisture, reduce runoff, filter air pollution and promote biodiversity by giving birds a place to nest.
By mandating green roofs, France also has an incentive to catch up to its European neighbors in solar development. As Think Progress points out, France lags behind solar giants like Germany, which has installed almost 40 gigawatts of photovoltaic capacity in its haste to ditch nuclear and fossil fuels. France, meanwhile, which predominantly relies on nuclear power, has only installed five GW of solar.