Written by: Corey Segal
Tokyo utilizes rooftop gardens to combat urban heat island effects! Introduced in 2001, the Nature Conservation Ordinance has prompted certain buildings to allocate rooftop space for plant growth: since 2009, private buildings over 1,000 square meters and public buildings over 250 square meters must meet at least 20% coverage; buildings over 5,000 square meters must exceed 25% green rooftop coverage. Today, over 1.8 million square meters are covered by rooftop foliage from over 5,700 buildings.
Rooftop foliage reduces rooftop and interior ceiling temperatures, in turn lowering energy costs during warmer months. Additionally, it also absorbs rainwater and reduces stormwater runoff, limiting strain on the city’s wastewater treatment facilities.
While Tokyo may have the most extensive law for implementing green rooftops, New York City similarly has implemented local laws to mandate the inclusion of rooftop plants into a building’s design. Local laws 92/94 state that new buildings or new roofs resulting from expansions of existing buildings must incorporate a green roof or solar photovoltaic cells that produce electricity. The city also requires all roofs to be cool roofs, meaning roofs that actively avoid materials which are more susceptible to absorbing solar radiation, for example, by being dark in hue.
The following other cities besides Tokyo and New York City have enacted green roof laws: Basel, Switzerland; Copenhagen, Denmark; Munich, Germany; Portland, Oregon; San Francisco, California; Toronto, Canada; and all of France. Hopefully we continue to see more cities across the world adopt green roofs into their building standards to not only create more energy efficient cities, but also more beautiful ones!
Sources:
https://www.kankyo.metro.tokyo.lg.jp/english/greenery
https://www.kankyo.metro.tokyo.lg.jp/english/greenery
https://happyeconews.com/tokyo-green-roof-law/
https://www.nyc.gov/site/buildings/codes/ll92-solar-green-roofs.page
https://guarinicenter.org/wp-content/uploads/2019/03/A-Review-of-Green-Roof-Laws-Policies.pdf