Despite being regularly shrouded in fog, the city of San Fransisco has made it mandatory for all new buildings of 10 storeys or less to have solar panels starting next year.
With the new rule, officials hope to cut 26,000 metric tons of carbon dioxide emissions annually, the equivalent of taking 5,500 cars off the road.
The ordinance was passed unanimously by San Francisco’s Board of Supervisors.
Currently most new builds in the state of California must have at least 15% of roof space "solar-ready" – meaning able to accommodate panels – but this rule requires actual installation.
Smaller municipalities in California, Lancaster and Sebastopol, already mandate rooftop solar systems, but San Fransisco is the first major city in the US to do so.
San Fransisco Supervisor Scott Wiener said: "By increasing our use of solar power, San Francisco is once again leading the nation in the fight against climate change and the reduction of our reliance on fossil fuels.
"Activating underutilised roof space is a smart and efficient way to promote the use of solar energy and improve our environment.
"We need to continue to pursue aggressive renewable energy policies to ensure a sustainable future for our city and our region."
Image: San Francisco and the Golden Gate Bridge (Wikimedia Commons/Bernard Gagnon)