California ADU Rules in 2026: What You Can Actually Build Now

California has amended its accessory dwelling unit statutes nearly every year for a decade, and another round took effect on January 1, 2026. What was true in 2019, or even in 2024, is often no longer true.

Here is where the law actually stands as of August 2026.

Your City Cannot Just Say No

The single most important thing to understand about ADU law is that approval is ministerial. There is no public hearing, no design review board, no discretionary finding, and no opportunity for a neighbor to object. If your application meets the objective standards, the agency approves it.

The permitting agency has 60 days from a complete application to approve or deny. SB 543, effective January 1, 2026, closed a major gap: an agency now has 15 business days to determine completeness, and if the application is incomplete it must provide a written list of what is missing within that same window. A resubmittal gets another 15-business-day review. Agencies must also provide a written appeal process for a denial, with a final determination due within 60 business days of the appeal.

Size Is Now Measured as Interior Livable Space

SB 543 also clarified that statutory square footage references for ADUs and JADUs now mean interior livable space, not gross area including wall assemblies. The practical effect is slightly more usable room than conservative local interpretations previously allowed.

The Baseline Your City Cannot Undercut

State law sets a floor no local ordinance can drop below:

- At least 800 square feet. Local lot coverage or floor area ratio cannot prevent an 800-square-foot ADU.

- Four-foot side and rear setbacks. A local ordinance cannot demand more than four feet from side and rear property lines.

- Sixteen feet in height for a detached ADU. That rises to 18 feet on a lot within half a mile of a major transit stop, plus up to 2 additional feet where the roof pitch matches the primary dwelling.

- Attached ADUs may reach 25 feet, or the height limit that applies to the primary dwelling in that zone, whichever is lower.

- Junior ADUs are capped at 500 square feet and are created within the walls of the single-family structure.

Many jurisdictions allow detached units up to 1,200 square feet. Confirm your local limit before schematic design.

You Are Probably Allowed More Than One Unit

SB 543 answered the stacking question directly: combinations are permitted. A lot with a single-family dwelling can have a converted ADU, a junior ADU, and a detached ADU. A multifamily lot can combine converted units inside the existing structure with detached units in the yard.

Impact Fees Have Hard Thresholds

Development impact fees may not be imposed on an ADU with 750 or fewer square feet of interior livable space, or on a junior ADU with 500 or fewer. An ADU or JADU at 500 square feet or less is also exempt from school impact fees. Design around those thresholds deliberately.

Owner Occupancy and Rental Terms

There is no owner-occupancy requirement for an ADU. A local agency may not impose one. For a junior ADU, owner occupancy applies only if the JADU shares a bathroom with the main house.

JADUs and ADUs approved under the statutory exempt categories must be rented for terms longer than 30 days. Local agencies may extend that restriction to other ADUs by ordinance.

Selling the ADU Separately

Under AB 1033, cities and counties may adopt an ordinance allowing an ADU to be sold separately as a condominium. This is permissive, not mandatory. Confirm the jurisdiction has actually adopted an AB 1033 ordinance before underwriting a property on that assumption.

Coastal Zone Projects Got Faster

AB 462, effective October 2025, requires local agencies with a certified local coastal program to approve or deny a complete coastal development permit for an ADU within 60 days. An ADU's coastal development permit can no longer be appealed to the California Coastal Commission.

Local Ordinances Are Under Real Pressure

Local agencies must submit adopted ADU ordinances to HCD within 60 days. Failing to do so renders the ordinance null and void in its entirety. If a city tells you its ordinance prohibits something state law protects, that is worth pushing back on.

New Construction Still Has to Meet the Energy Code

The ADU statutes do not relax Title 24. A new detached ADU is new residential construction and the 2025 energy code cycle applies. Plan for envelope, mechanical, and electrification requirements early — they shape the design rather than getting layered on at the end.

As a licensed architect, CASp #1063, LEED AP BD+C, and licensed general contractor, Avila Architects provides ADU design, accessibility consulting, and construction services throughout California. If you are evaluating a property or planning an ADU, we can tell you what your lot will actually support before you spend money finding out.

Requirements described here are current as of August 2026 and reflect California state law. Local ordinances vary by jurisdiction. This article is professional information and is not legal advice.

‍