The ADU Permit Process at a Glance
The California ADU permit process runs in seven stages: verify site eligibility, prepare design drawings, submit a complete application, pass plan review (local agencies have up to 60 days under state law once a complete application is received), receive your permit, pass construction inspections, and obtain a certificate of occupancy. Most projects take 6 to 18 months from first design meeting to occupancy, depending on ADU type and local workload.
Before You Apply: Check Your Property First
Before any designer produces drawings, your property needs a basic eligibility check. This step costs nothing and can prevent months of wasted work.
California state law (now codified in Government Code §§66310–66342, reorganized from the original §65852.2) sets minimum standards that all cities and counties must allow. Single-family properties can have one ADU and one Junior ADU (JADU). Multifamily properties have different allowances based on existing unit count. For a full overview of what state law requires and what local governments can still restrict, read the California ADU laws guide.
Key items to confirm before hiring a designer:
Zoning: Confirm your property is zoned for residential use and that ADUs are permitted in your zone.
Setbacks: State law sets a 4-foot rear and side setback for most new detached ADUs. Flood zones, fire hazard areas, and coastal zones may have stricter setbacks.
Lot coverage: Each jurisdiction limits what percentage of your lot can be covered by structures. Adding an ADU counts toward that limit.
Utility capacity: Existing water, sewer, and electrical service may need upgrading to support a new unit. A rough assessment early prevents surprises during plan review.
The ADU Permit Process: Seven Stages
- 1
Hire a Designer or Architect
ADU permit applications require professionally prepared drawings. Most building departments will not accept hand-drawn plans or informal sketches. You need a licensed architect, architectural designer, or ADU design-build firm to prepare a complete plan set.
The design package typically includes a site plan showing property boundaries and ADU placement, floor plans with dimensions and room labels, exterior elevations showing all four sides, a California Energy Code (Title 24) compliance report, and structural calculations if the project involves new construction or significant structural work.
- 2
Prepare Your Application Package
"Complete application" has a specific legal meaning under California ADU law. Once your application is deemed complete, the 60-day review clock begins. An incomplete submission delays that clock and adds time to your overall project.
Beyond design drawings, a complete application typically includes a completed permit application form, applicable plan check fees, proof of property ownership or authorization to apply, the Title 24 energy compliance report, and any supplemental forms required by your specific jurisdiction. Your designer should know your local building department's submittal checklist.
- 3
Submit to Your Local Building Department
Which department you submit to depends on where your property sits. City parcels go to that city's building department. Properties in unincorporated county areas go to the county building department. In San Diego, city residents apply through the City of San Diego Development Services Department (DSD); unincorporated parcel holders apply to San Diego County.
Many jurisdictions accept applications online. Once submitted, the agency has 30 days to notify you if anything is missing. If they don't, the application is deemed complete and the 60-day clock starts. Applications using preapproved ADU plans — which all California jurisdictions were required to offer starting January 1, 2025 — qualify for a 30-day review instead of 60.
- 4
Plan Review
Plan review is when the building department evaluates your drawings for code compliance. Reviewers check building code requirements, energy code (Title 24) compliance, fire and life safety provisions, plumbing and electrical adequacy, and applicable zoning standards.
Most ADU projects go through one to three rounds of corrections before plans are approved. A well-prepared plan set that addresses common issues upfront — ceiling height, fire separation, egress, and energy compliance — reduces correction rounds. Your designer should respond to any correction letters promptly and completely.
- 5
Permit Issuance
Once plans are approved and permit fees are paid, the building department issues your permit. This document authorizes construction to begin. Do not break ground before the permit is in hand.
The permit package includes the approved plan set with stamps, a list of required inspections, and instructions for scheduling inspections during construction. Some projects also require separate grading, demolition, or encroachment permits for utility work in the public right-of-way. Your contractor should confirm which additional permits apply before any work starts.
- 6
Construction Inspections
Inspections happen at specific milestones during construction, not just at the end. Each inspection must pass before the next phase of work proceeds. Skipping inspections — or covering work before it is inspected — will prevent your ADU from receiving a certificate of occupancy.
- 7
Certificate of Occupancy
After the final inspection passes, the building department issues a certificate of occupancy (CO). The CO is official documentation that the ADU was built as permitted and is safe for habitation. Without it, the unit cannot legally be occupied or rented.
The CO matters beyond legality. Homeowners' insurance coverage on the unit may depend on it. Lenders ask for it during refinancing. Buyers and their agents will ask for it at resale. Getting a CO from the start protects your investment.
Construction Inspection Stages
The number and type of inspections depends on your project scope. For most ADU projects, expect inspections at the following milestones:
Foundation or slab
Inspected before concrete is poured. For garage conversions, this may include verifying slab thickness, vapor barrier installation, and reinforcement.
Rough framing
After structural framing is complete but before insulation or drywall is installed. The inspector checks that framing meets structural requirements, blocking is correct, and openings are properly sized.
Rough electrical, plumbing, and mechanical
All new wiring, pipes, and HVAC rough-in must be inspected before walls are closed. This inspection cannot be skipped — covering work before inspection almost always requires opening walls later.
Insulation
Required before drywall is installed. Insulation must meet Title 24 energy code requirements for wall, ceiling, and floor assemblies.
Drywall
Some jurisdictions require a separate inspection at this stage; others roll it into the insulation or framing inspection. Confirm with your building department before closing walls.
Final inspection
Done after all construction is complete, fixtures are installed, and the unit is ready for occupancy. A passed final inspection is what triggers the certificate of occupancy.
Note: Inspection requirements vary by jurisdiction and project scope. Your building permit paperwork will list the specific inspections required. If you are unsure whether a phase of work needs inspection before it proceeds, contact your building department before covering anything.
How Long Does the ADU Permit Process Take?
Timeline estimates vary by ADU type, existing property conditions, and local building department workload. The ranges below reflect typical California projects and individual projects may fall outside them.
| ADU type | Design | Permitting | Construction | Total estimate |
|---|---|---|---|---|
| Junior ADU (JADU) | 1–2 mo | 1–2 mo | 2–4 mo | 3–6 months |
| Garage conversion | 1–3 mo | 1–3 mo | 2–5 mo | 4–9 months |
| Attached ADU | 2–3 mo | 2–4 mo | 4–8 mo | 8–14 months |
| Custom detached ADU | 2–4 mo | 2–5 mo | 6–14 mo | 12–20+ months |
Timeline note: These are general estimates. Actual timelines depend on your city or county's current workload, how many correction rounds your plan set requires, contractor scheduling, and whether utility upgrades are needed. For San Diego-specific timing, read the San Diego ADU permit guide.
Common Permit Delays (and How to Avoid Them)
Most ADU permit delays are preventable. The majority trace back to a handful of recurring problems.
Incomplete application package
The most common cause of delay. If your application is missing documents, the 60-day clock never starts. Review your jurisdiction's submittal checklist before submitting, or work with a designer who already knows it.
Missing or incomplete Title 24 energy compliance report
California's Energy Code requires a compliance report for all new and converted residential space. It must be prepared by a certified energy consultant using compliant software. Missing this document is one of the most common reasons for plan check corrections.
Structural calculation errors or omissions
New detached ADUs require engineered structural drawings. Garage conversions with modifications to the roof or walls may also require structural review. Errors in these drawings generate correction letters and delay approval.
Fire department holds
Projects with fire sprinkler requirements or fire access issues may need a separate fire department review running concurrently with building plan check. A fire hold can extend the overall timeline beyond the 60-day window.
Utility upgrade requirements
If the building department determines your existing utility connections are insufficient, they may condition permit issuance on upgrades. Water, sewer, and electrical upgrades can each add weeks to the pre-construction phase.
Contractor scheduling gaps
A common oversight: securing a permit before a contractor is actually available. If your contractor is booked out several months, fees may lapse and permit conditions may need re-review. Confirm contractor availability before submitting.
Homeowner Checklist
Use this as a starting point before engaging designers, builders, or submitting any paperwork.
Verify property zoning, setbacks, and lot coverage allow an ADU before hiring a designer
Hire a licensed architect or designer with ADU experience in your specific jurisdiction
Confirm which building department has jurisdiction over your parcel (city vs. county)
Ask your jurisdiction whether preapproved ADU plans are available — they qualify for a 30-day review
Submit a complete application package; incomplete submissions delay the 60-day clock
Budget time (not just money) for correction rounds — plan for one to three rounds
Confirm no construction work starts before the permit is physically in hand
Schedule all required inspections at each construction milestone — never cover work before inspection
Final Thoughts
The ADU permit process in California is more predictable than many homeowners expect, once you understand the stages. State law protects applicants with binding timelines: a complete application must receive a decision within 60 days, and agencies cannot stall indefinitely on completeness reviews. What causes most project delays is not the system — it is incomplete submittals and under-prepared plan sets.
Hiring a designer and contractor already familiar with your local building department's requirements makes a measurable difference. A plan set that anticipates common correction issues and submits clean the first time can shave months off a project that otherwise cycles through multiple rounds of back-and-forth.
For project-specific guidance, the garage conversion guide for San Diego covers San Diego-specific permit requirements, parking rules, and common construction challenges. The detached ADU guide for San Diego addresses setbacks, costs, and typical construction timelines for new builds.
Frequently Asked Questions
Does the 60-day review clock start when I submit my application?+
Can my ADU permit be denied if I comply with all state standards?+
Do I need separate permits for electrical, plumbing, and mechanical work?+
What happens if I start construction before my permit is issued?+
How many inspections will I need during ADU construction?+
What is a certificate of occupancy and why does it matter?+
Disclaimer: This article is for informational purposes only and does not constitute legal, zoning, permitting, engineering, or construction advice. ADU permit requirements, timelines, and processes vary by city, county, project type, and property conditions. California ADU law updates frequently. Confirm current requirements with your local building department and consult qualified ADU professionals before making decisions about your project.
Sources and Official Resources
- •California Government Code §§66310–66342 — ADU provisions (reorganized from §65852.2) — California Legislature. leginfo.legislature.ca.gov. Last reviewed July 2026.
- •ADU State Laws Summary and Checklist (July 2025) — Association of Bay Area Governments (ABAG). abag.ca.gov. Comprehensive summary of current California ADU statutory requirements including 60-day and 30-day review timelines.
- •California Department of Housing and Community Development — ADU Handbook — California HCD. hcd.ca.gov. Last reviewed July 2026.
- •City of San Diego Development Services Department — Information Bulletin 400: Accessory Dwelling Units / Junior Accessory Dwelling Units — City of San Diego DSD. sandiego.gov/development-services. Last reviewed July 2026.
- •California Building Code (Title 24, Part 2) — California Building Standards Commission. dgs.ca.gov. Residential construction inspection requirements.
- •California Energy Code (Title 24, Part 6) — California Energy Commission. energy.ca.gov. Residential energy compliance requirements for ADU construction.
This guide draws on official California state law provisions and government agency resources current as of July 2026. ADU regulations change frequently. Always verify requirements with the applicable building department and consult qualified professionals before starting a project.