California has made accessory dwelling units significantly easier to permit over the last several years. State law now pre-empts many local restrictions, ministerial approval is required for code-compliant ADU applications, and cities cannot deny a permit based on parking requirements alone in most cases. Despite these protections, ADU permit applications still get delayed or returned for corrections. Understanding the process in advance prevents most of those delays.
Types of ADUs in California
California recognizes several ADU configurations, each with different requirements.
Attached ADU. An addition to the primary dwelling that creates a separate unit with its own entrance. The addition must comply with setback requirements, though state law restricts how restrictive local setbacks can be.
Detached ADU. A separate structure in the rear yard or side yard. California law allows detached ADUs up to 1,200 square feet and limits setback requirements to four feet from rear and side property lines in most cases.
Junior ADU (JADU). A unit created within the existing primary dwelling, typically from a bedroom or attached garage. JADUs are capped at 500 square feet and require an owner-occupancy covenant recorded against the property.
Garage Conversion ADU. An existing attached or detached garage converted to habitable space. California law prohibits cities from requiring replacement parking for garage conversions in most circumstances.
What the Permit Process Looks Like
Pre-Application Research
Before any drawings are prepared, the project team should confirm the following with the applicable building department or through a pre-application meeting:
- Whether the property is in a design review overlay or historic district that may apply additional requirements
- The applicable building code cycle (California adopts codes on a different schedule than some cities)
- Any local ADU ordinance provisions that remain permissible under state law
- Utility connection requirements for the new unit
Drawing Package Requirements
A California ADU permit set typically includes:
- Site plan showing the existing structures, proposed ADU location, setbacks from all property lines, lot coverage and FAR calculations, and utility connections
- Floor plans for both the existing dwelling and the proposed ADU
- Exterior elevations of the proposed ADU from all sides
- Building section through the ADU
- Construction details for any new assemblies (foundation, framing, waterproofing)
- Structural drawings and calculations if the project involves new structural work
- Title 24 energy compliance package (required for all new construction and most conversions)
- CalGreen checklist
Some jurisdictions also require a soils report, a grading and drainage plan, or specific life safety documentation depending on the scope.
Plan Check and Review Period
California law requires building departments to act on a complete ADU application within 60 days. If the application is deemed incomplete, the department has to notify the applicant within 30 days of submission with a list of what is missing.
Ministerial approval means the department cannot exercise discretion. If the project complies with state ADU law and local codes, the permit must be issued. Design review, planning commission approval, and neighbor notification are not permitted for most ADU types under state law.
The actual plan check timeline varies by jurisdiction and is heavily dependent on staffing. High-volume departments like Los Angeles, San Diego, and the Bay Area counties frequently have over-the-counter review for straightforward ADU applications, which can significantly accelerate the timeline.
Common Plan Check Corrections
Despite ministerial approval requirements, ADU applications frequently return from plan check with corrections. The most common issues are:
Incomplete site plan. Missing setback dimensions, lot coverage calculations that do not close, or utility connection lines not shown.
Missing Title 24 documentation. Title 24 compliance is required and cannot be deferred. The compliance report needs to be submitted with the permit application.
Insufficient structural documentation. Garage conversions and additions that involve structural modifications often require engineer-stamped drawings and calculations. Applications submitted without them are returned as incomplete.
Owner-occupancy covenant not provided for JADUs. JADUs require a recorded owner-occupancy covenant prior to permit issuance. Some departments require evidence of the covenant submission with the application.
What Affects Timeline
The biggest factors affecting ADU permit timeline are:
- Whether the application is submitted as complete on the first round
- The building department's current backlog (this varies significantly)
- Whether the project is in a jurisdiction with over-the-counter ADU review
- Whether plan check corrections require significant design changes or just documentation revisions
A well-prepared application with complete drawings, coordinated structural documentation, and a Title 24 package submitted from day one consistently moves faster than applications that work through a correction cycle.
How CADTRI Approaches ADU Packages
CADTRI prepares ADU permit packages with jurisdiction-specific research before any drawings begin. We confirm the applicable setback rules, lot coverage limits, and submittal checklist for the specific city or county, build the package to those requirements, and coordinate Title 24 documentation alongside the architectural drawings.
If you have an ADU project ready to permit, request a proposal and we will confirm what the jurisdiction requires and what the timeline looks like.