What permits are required to build an ADU in California?

Every Accessory Dwelling Unit in California requires a building permit — there is no size or type exemption, even for a small studio or a JADU carved out of an existing bedroom. The building permit is the master approval that triggers plan review and bundles together the structural, electrical, plumbing, mechanical, and energy-compliance scopes. Around that core permit sit several other approvals you should understand before you submit.

The permits and approvals in a typical ADU package

• Building permit — the primary permit covering the ADU structure and all building systems. This is what plan check reviews and what your inspector references at each construction stage.
• Planning / zoning approval — ADUs are approved ministerially in California, meaning no public hearing and no discretionary design review as long as the project meets objective zoning standards (setbacks, height, lot coverage). Staff-level zoning review usually runs concurrently with the building permit.
• Electrical, plumbing, and mechanical permits — depending on the city, these are either separate trade permits pulled by your licensed electrician (C-10), plumber (C-36), and HVAC contractor (C-20), or they are reviewed as scopes folded into the single building permit.
• Title 24 energy documentation — a registered CF1R is submitted with the building permit application; without it the application is incomplete. See Title 24 Reports.
• Utility service applications — separate from the building permit. Water, sewer, gas, and electric service requests are filed with your utility (PG&E, SCE, SDG&E, LADWP, or your local water/sewer district) and run on their own timelines.

Why the distinction matters for your schedule

The 60-day statutory review clock under California law applies to the building permit once a complete application is on file. Utility coordination is a completely separate track and is frequently the longest item on the project schedule — a panel upgrade or new service connection can take weeks to months depending on the provider. The single most common scheduling mistake we see is starting utility coordination only when construction is nearly finished. Start it the same week you submit for permit.

What does not require a separate permit

Under recent state reforms, cities must process certain related work as part of the ADU permit rather than as standalone permits. For example, removing a garage door and closing the opening for a garage conversion is handled within the ADU building permit, not a separate demolition permit. Requirements and local ordinances vary by jurisdiction, and ADU law changes frequently — confirm the exact permit bundle with your local building department before you file.

A practical pre-submittal checklist

1. Confirm your lot is zoned for an ADU and identify setback, height, and size limits.
2. Have architectural, structural, and MEP plans prepared and coordinated.
3. Obtain a registered Title 24 CF1R for your climate zone.
4. Open utility service requests early.
5. Submit a complete package so you pass the completeness review and start the 60-day clock immediately.

If you want the engineering portion handled correctly from the start, our Full MEP Package delivers permit-ready mechanical, electrical, and plumbing sheets coordinated with your architectural set. See the California ADU permit guide for the full process.