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 law, going into effect in January, will require between 15 to 30 percent of roof space on most new construction projects to incorporate solar, green roofs, or a blend of both.

The ordinance builds on an earlier bill passed by the city’s Board of Supervisors in April that requires new residential and commercial buildings 10 stories or shorter to install solar panels or a