The National Geographic news has written about another San Francisco first:

This week, San Francisco became the first U.S. city to require that certain new buildings be built with a green roof—an eco-friendly design technique that sows plants above a roofline. This latest action builds on a growing trend that has taken root around the world, and which boosters say offers significant benefits for the planet.

The new by-law enacted in January 2016 will mean that 15 to 30 per cent of roof space on new office construction projects must  incorporate solar, green roofs, or both. An earlier by-law requires new residential and commercial buildings under ten storeys to install solar panels or a solar heating system with fifteen per cent roof coverage.

Green roofs reduce stormwater runoff, improve air quality, and help mitigate the urban heat island effect. For building tenants and owners, green roofs reduce the need for heating and cooling. They also can provide food and a recreational area for residents. Combining solar panels and green roofs can actually make each component work better. Solar panels can provide shade for plants and grasses, reducing the need for watering, while the panels work best when they are cool (green roofs can help lower temperatures compared to conventional ones).

Other cities such as Chicago has already planted their city hall roof, lowering summer temperatures in the building. Bonn Germany has led the green roof innovation and been an early adapter to this roof form in Europe.

Green roof legislation is being passed around the world. Cordoba became the first city in Argentina to require green roofs in July. France’s new legislation mandates at least partial coverage of green roof or solar technology on all new construction and goes into effect next March. In 2009, Toronto mandated green roofs on industrial and residential buildings. Germany’s green roof industry has been legislated and supported by the government in various ways since the 1970s.

There are approximately 25 North American cities that support green roofs to some extent, from bigger cities to medium and smaller communities like Syracuse and Port Coquitlam in British Columbia. Washington D.C. has a de facto requirement for large buildings through its stormwater regulations. New York City has tax abatements.

Valuable green building certifications, such as LEED, also award points for green roofs, so they are popping up across the country even without legislation. Green roofs offer an environmental solution and provide a range of benefits as regional climates become hotter and populations in cities continue to grow. Kudos to San Francisco for showing the way forward.