For decades, California has led the country in its commitment to clean energy production and energy reduction, adopting solar rebate and net metering programs, and regularly updating its 30-plus-year-old energy efficiency standard, Title 24. Ever the trendsetter, on May 9, the California Energy Commission (CEC) voted 5-0 to require all new homes to have rooftop solar power, making it the first state in the country to enact such a mandate.

The requirement covers all low-rise residential buildings, but only applies to new construction built after January 2020. Construction companies have a few options to meet the mandate. Every home must have rooftop solar panels, access to a community solar project or, in cases where solar is not suitable, provide energy efficiency upgrades that compensate. (There are some exceptions for homes in particularly shaded spots.) In addition to solar panels, the mandate also requires additional energy efficiency provisions such as raising the standards for insulation, water heaters and air conditioners.

The state energy commission says it has been preparing for this transition for years, pointing to regular updates to the energy code and a 2013 requirement that all new homes be solar-ready. According to a CEC spokesperson it’s all part of an initiative to reduce greenhouse gas emissions 40 percent by 2030. The state has another aggressive goal (adopted in 2007) for new residential buildings to be net-zero energy by 2020, followed by all new commercial construction by 2030.

In contrast to the commission’s limited debate and unanimous vote, opponents have raised concerns about the increased home building costs in a state already struggling with an affordable housing shortage. A report commissioned by the state found that the solar panels along with the other energy-efficient provisions would raise the average upfront cost of a home by nearly $10,000.

Those who support the bill argue that what homeowner’s save on utility bills will balance this out in the long run. Solar panel leasing, in which homeowners have access to the energy while the company maintains the system, provides another option to spread out the upfront cost. Still rooftop solar generates energy at a much higher cost than solar farms, which benefit from a larger scale lowering the cost of energy production.

After the CEC’s vote, the requirements will be passed to the California Building Standards Commission, where it is expected to be ratified.