In a national first, the City of San Francisco has mandated that all new residential and commercial buildings of 10 stories or less must have at least 15% of their roofs covered by solar panels. The Board of Supervisors voted unanimously in favor of the measure this week.

The law proposed by Supervisor Scott Wiener targets reliance on fossil fuels and will come into effect at the start of 2017, according to the San Francisco Business Times.

The new law builds on an existing California law that requires 15% of roofs be solar-ready (able to host solar panels), Wiener wrote in a Medium post. Under the new measure, developers will have to install either “photovoltaic or solar water panels” in this space.

The law has been supported by the US Green Building Council and the Building Inspection Comission, among others.

San Francisco has previously committed to overarching sustainability targets. These include 0% landfill waste, 50% non-automobile transportation (including public transportation and biking) and 100% renewable energy. [SFBT]