California has become the first state in the country to require that all new homes be built with solar panels. The mandate is aimed at reducing California’s overall greenhouse gas emissions.

The California Energy Commission voted unanimously to recommend energy efficiency standards that are set to be added to state building standards later this year, effecting all construction after January 1, 2020. Under the new rules, builders will be required to either build each new home with its own solar power system or build a shared solar power system to serve a group of homes. In addition to single family homes, the requirement will also apply to apartment and condominium complexes of three stories or less.

The solar panel rule next goes before the California Building Standards Commission (CBSC), which typically adopts recommendations from the energy commission. CBSC is expected to take up the matter in October or November.