California's Building Energy Efficiency Standards (California Code of Regulations, Title 24) — establishes minimum insulation, window, HVAC, lighting, and renewable-energy requirements for new construction including ADUs.
All new ADUs must meet Title 24. From 2026, detached ADUs over 250 sqft are subject to mandatory solar requirements (with limited exceptions). Title 24 compliance documentation is part of every ADU permit application.
Part of the BackyardADU California ADU Glossary — plain-English definitions of the regulatory, construction, and financing terms you'll encounter during a California ADU project.