What are California ADU requirements?

California ADU (Accessory Dwelling Unit) requirements are a set of statewide standards — written into state law and the California Building Standards Code — that limit how cities can regulate ADUs, plus the building, energy, and utility rules every unit must meet. Statewide minimums apply, but local ordinances and lot conditions vary, so always confirm the specifics with your local building department.

The statewide framework

California has spent the last several years steadily pre-empting restrictive local ADU rules. The result is a baseline that every jurisdiction must honor, even if its own zoning code says otherwise:

• Ministerial approval — qualifying ADUs are approved over the counter without a public hearing or discretionary design review, and complete applications must be acted on within statutory timelines.
• Protected size and height — cities must allow at least an 800 SF ADU and a minimum 16-foot height, regardless of local lot-coverage or floor-area limits.
• Reduced setbacks — new detached ADUs need only 4-foot side and rear setbacks, and conversions of existing legal space require no additional setback.
• No owner-occupancy requirement for standard ADUs, so you can rent both the main house and the ADU.
• Impact-fee relief for smaller units under applicable size thresholds.

What your ADU must include

Beyond zoning, an ADU is a complete, independent dwelling and must be built like one. Core requirements include:

• Independent utilities — its own (or properly sized shared) electrical, water, and sewer service, sized by calculation.
• Title 24 energy compliance — a registered CF1R energy report for the permit, plus HERS field verification of the installed systems.
• Permit-ready MEP plans — mechanical, electrical, and plumbing drawings that document the HVAC, panel/circuits, and water/waste systems.
• Complete living facilities — a kitchen, a full bathroom, sleeping area, and a permanent heating system capable of maintaining 68°F.

A quick orientation checklist

1. Confirm your parcel's zoning, climate zone, and any local reach codes (such as all-electric mandates).
2. Verify the maximum size your lot allows — never less than the protected 800 SF minimum.
3. Check setbacks: 4 ft side/rear for new detached, none added for conversions.
4. Plan for independent utilities and a load calculation early — utility coordination is often the longest item on the schedule.
5. Budget for Title 24, and check whether solar applies to your project type.

Rules change between code cycles, so treat this as a starting map rather than a final answer. For a deeper walkthrough, see our California ADU Permit Guide and the Complete ADU MEP Guide. When you're ready for permit-ready drawings, our Full MEP Package starts at $1,495 and scales with square footage.