The California Building Standards Commission on Wednesday unanimously upheld a May 9 decision to require solar panels on homes up to three stories. The requirement goes into effect Jan. 1, 2020.

Currently, just 9% of single-family detached homes in California have solar panels. But as the state pushes toward decreasing greenhouse gas emissions—and with a 2045 goal to transition to a fully renewable energy grid devoid of fossil fuels—this rule will help accelerate that progress. Aside from energy efficiency, solar panels reduce ozone-damaging household emissions, most of which come from natural gas-generated electricity.

In the long-term, solar panels benefit homeowners. While the upfront cost for building a home will increase—by as much as $10,000, according to the California Energy Commission, or as much as $25,000-30,000, according to home construction company Meritage Homes—long-term energy bill savings will be considerable.

Reuters reports that a homeowner could expect to save $19,000 in energy costs over 30 years, while Meritage Homes predicts reduced operating costs could amount to as much as $50,000-60,000 over a 25-year period.

A senior scientist with the Natural Resources Defense Council, meanwhile, argues the solar-panel mandate “won’t necessarily make homes more expensive to buy. What they will do is save money on utility costs. This is not only the right thing to do for the climate, it is financially smart.”

California’s Building Standards Commission’s final approval of the home solar rules follows action in May by the California Energy Commission to include the change in the state’s Green Building Standards Code.

“With extreme weather events becoming more frequent, there is even greater need for homes that are efficient, reliable and resilient,” Drew Bohan, executive director of the energy commission, explained. Rules such as these, he said, “will continue to keep costs down, better withstand the impacts of climate change, and reduce greenhouse gas emissions.”