ADU Design in Patterson, CA

ADU Design in California: what governs your project

California has the nation's most developed ADU framework: a series of state laws since 2016 require cities to approve ADUs ministerially within 60 days, cap impact fees (none allowed on ADUs under 750 square feet), and allow up to 1,200-square-foot detached units. The 2024 legislation expanded options further, including separate sale of ADUs as condominiums and pre-approved plan programs.

Energy code

Approvals are by-right and ministerial statewide, but building permits, Title 24 energy compliance, and utility connections still apply. Parking mandates are prohibited near transit, and fire sprinkler requirements follow the primary dwelling's status.

Permitting & plan check

Large cities like Los Angeles, San Diego, and San Francisco run large plan-check departments with published correction cycles; LA's LADBS process is known for thorough multi-round review. Many smaller cities contract building plan review to third-party firms. Title 24 energy compliance documentation is a standard part of every commercial permit submittal.

Good to know

• California's Title 24 Energy Code is among the strictest commercial energy codes in the US.
• Most of urban California designs for high Seismic Design Categories with near-fault considerations.
• Construction stormwater statewide is covered by the State Water Board's Construction General Permit.

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