California’s Building Standards—collectively known as Title 24—are updated on a triennial cycle. The current 2022 codes will transition to the 2025 edition, which becomes mandatory for most projects submitted on or after January 1, 2026. As with prior cycles, the 2025 codes are based on national model codes, modified with California-specific amendments addressing seismic safety, wildfire risk, climate goals, and housing needs.

As California continues to lead the way in energy-efficient housing, homeowners looking to build an Accessory Dwelling Unit (ADU) must navigate a growing list of sustainability requirements—including solar panel mandates. While Title 24 of the California Energy Code has made solar systems mandatory for new single-family residences (SFRs), the rules surrounding ADUs are more nuanced. Whether you are legalizing an existing unit, constructing an addition to an SFR, converting existing space, or building a new detached ADU will determine whether solar panels are required.

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