San Diego ADU Ordinances Explained: 2026 Rules, Setbacks and Updates

Knowing Which Rules Actually Govern Your Lot

Your parcel's jurisdiction determines which ADU rules apply — not just the city you think you live in.

State ADU law establishes minimums: what cities must allow, and what they can't restrict. Local ordinances — such as the City of San Diego's Municipal Ordinance MO-21-0001 and its 2025 amendments — add provisions on top. Setback distances, height allowances, size maximums and design standards can all differ from a general California ADU summary.

The City of San Diego, Carlsbad, El Cajon and unincorporated San Diego County each administer their own distinct ADU ordinance. A property in unincorporated county falls under the County's 2026 ADU Zoning Ordinance, not the City's. Projects designed against the wrong jurisdiction's ordinance can require a complete redesign before approval.

Sheiner Construction operates across all these jurisdictions. We verify exactly which ordinance governs your parcel before any design drawings are produced.

Building codes, permit requirements and state housing law are amended on a regular cycle. Confirm current requirements for your parcel with the relevant authority before relying on them for design or budget decisions.

From AB 68 to the 2026 Updates — Translated

State law changed. San Diego's local ordinances evolved. The details determine what you can build.

Owner-occupancy (permanently abolished)

Thanks to AB 976, California permanently eliminated the owner-occupancy requirement for standard ADUs. A San Diego property owner does not need to live on the lot to build an ADU or rent it out.

One exception: Junior ADUs, units of up to 500 sq ft created within the walls of an existing primary residence, only require owner-occupancy if they share sanitation facilities with the primary home. If the JADU has its own bathroom, it operates like a standard ADU.

Selling your ADU — the 2026 AB 1033 update

In March 2026 the San Diego County Board of Supervisors voted unanimously to adopt AB 1033 for unincorporated county areas. This allows homeowners in unincorporated communities to legally separate their ADU from the primary home and sell it as a condominium.

Setback rules and fire zones

Detached ADUs of 800 square feet or less may qualify for reduced rear and side setbacks, typically 4 feet. As of August 2025 the City of San Diego requires strict 4-foot to 5-foot setbacks for ADUs located within High or Very High Fire Hazard Severity Zones to comply with defensible space requirements.

Size limits and the 2025 two-story cap

California law requires cities to allow ADUs of at least 800 square feet regardless of lot coverage restrictions. The City Council rolled back larger incentives in mid-2025, and as of August 2025 the maximum story count for ADUs on single-family lots in the City of San Diego is capped at two stories, even where underlying zoning would allow taller structures.

Utility fee reform under AB 68

ADUs under 750 square feet are generally exempt from, or face significantly reduced, water and sewer connection fees. Larger ADUs may still face full connection fee schedules. Some homeowners purposely design a 749-square-foot ADU specifically to stay below the threshold.

Ministerial approval and faster reviews

California law requires cities to approve qualifying ADU applications through a ministerial review process, meaning local building departments cannot deny a compliant application for subjective reasons like aesthetics or neighbourhood character. Under SB 543, local agencies must review your application and provide a written list of missing items within 15 business days.

How These Rules Play Out on San Diego Parcels

Real parcel conditions create situations the rule tables don't fully anticipate.

• The coastal lot with a narrow rear yard: standard setbacks would make the rear yard too shallow for a detached ADU. The 4-foot setback reduction makes the unit feasible — but only if the ADU is 800 square feet or less and no utility easements run along the rear property line.
• The El Cajon parcel governed by its own rules: El Cajon has its own ADU ordinance. It complies with state minimums but has different design standard provisions and a separate review process. A design produced against City of San Diego parameters would require a complete redesign.

Reading the Ordinance Versus Knowing the Parcel

The most common gap I see on ADU projects isn't a design problem. It's a jurisdiction problem.

I'm Joseph Sheiner. I've been managing ADU construction projects in San Diego since 2012 under CSLB License #1083621.

Homeowners research general California ADU law and start planning around those numbers. Then the parcel turns out to be in an unincorporated county zone where AB 1033 allows condo sales, or in a City of San Diego fire hazard zone requiring specific defensible setbacks. I verify the applicable ordinance before any design drawings are produced.

State law summaries tell you what California requires cities to allow. They don't tell you what your parcel can accommodate.

Joseph Sheiner, Founder

Frequently asked questions