When does an ADU get a certificate of occupancy in California?

An ADU gets its certificate of occupancy after construction is finished and every required inspection has passed, and you need it before anyone lives in the unit. State law also says the ADU's certificate cannot be issued before the main house's certificate, except in specific disaster situations.

What a certificate of occupancy is

HCD's ADU Handbook describes a certificate of occupancy as the document a local building department issues certifying that a newly constructed residential building has been inspected for compliance with the California Building Standards Code and local ordinances, and it states that you must obtain one before any residential occupancy of an ADU or JADU. Local practice varies in how occupancy approval is documented, especially for conversions, so ask your building department what you will receive at the end of your project.

The sequencing rule

Government Code section 66328(a) bars a local agency from issuing a certificate of occupancy for an ADU before it issues one for the primary dwelling. This matters most when you build a new house and an ADU together, or when the main house is under major construction. Disaster exceptions exist: AB 462 (effective October 10, 2025) requires issuance for a detached ADU first in a county covered by a Governor's emergency proclamation made on or after February 1, 2025, when the main home was substantially damaged or destroyed by that event and the ADU has its permits and has passed all required inspections. A separate executive order covers properties damaged in the January 2025 Eaton and Palisades fires.

What usually happens before you get it

1. Foundation and rough inspections of framing, electrical, plumbing and mechanical work before walls are closed.
2. Insulation and energy-related inspections, plus any field verification the Title 24 documents require.
3. Sign-offs from other agencies on your permit's referral list, such as fire or utilities, where applicable.
4. Final inspections for every trade, confirming the work matches the approved plans.

Garage conversions and occupancy classification

Under section 66314(d)(8), building an ADU does not by itself count as a Group R occupancy change under the local building code unless the building official makes a written finding, based on substantial evidence, of a specific adverse impact on public health and safety. The same provision lets the agency change the occupancy classification of space that was uninhabitable or permitted only for nonresidential use, such as a garage, when it is converted to living space. That is one reason converted garages are inspected as dwellings.

What this means for your MEP plans and permit set

Final inspection is where the installed work is compared with the approved MEP drawings and Title 24 report. An equipment swap, a relocated panel or a different water heater can hold up the final sign-off until a revision is approved. Keep your plans current with what is actually installed. See what happens if HVAC is installed differently than shown, inspections for garage conversions, and the California ADU permit guide. Confirm your local occupancy process with your building department.

Sources: leginfo.legislature.ca.gov, leginfo.legislature.ca.gov, hcd.ca.gov, planning.lacounty.gov.