ADU Permit California: Cost, Process & Timeline (2026)

An ADU permit in California costs between $3,000 and $15,000 depending on your city. That’s the line item most homeowners fixate on — and the one some try to skip. Building without a permit is a code violation under California Building Code Section 105.1, and the consequences are not abstract: stop-work orders, daily fines, mandatory demolition orders, and structures that can’t be legally rented, insured, or included in a property appraisal. Retroactive permitting — if your city even allows it — typically costs two to three times the original permit fees because finished walls have to be opened for inspection. The permit is the cheapest part of the project.

This guide covers the actual ADU permit process in California — fees by city, realistic timelines, common rejection reasons, and the steps between application and final inspection.

California’s ADU laws establish statewide rules that every local jurisdiction must follow. The state sets the floor — cities can make the process easier but cannot make it harder. Here’s what state law guarantees:

• Every single-family lot can have at least one ADU and one JADU
• 60-day approval deadline — your city must approve or deny a complete ADU application within 60 days
• No parking requirements for ADUs, including garage conversions
• No owner-occupancy requirement for standard ADUs (JADUs may require it)
• Reduced or waived impact fees for ADUs under 750 sq ft
• Detached ADUs up to 1,200 sq ft are allowed regardless of lot size or floor area ratio
• 4-foot setbacks for detached ADUs (rear and sides)

These rights exist because of state law. If a local building department tells you otherwise, they’re either wrong or working from outdated regulations. The California Department of Housing and Community Development (HCD) enforces compliance and has overridden local jurisdictions that impose illegal restrictions.

Step 1: Feasibility Check (Week 1)

Before you spend money on plans or engineering, confirm that your property is eligible and identify any site-specific complications.

• Zoning verification: Confirm your property is zoned for residential use. Most single-family residential zones (R-1, RS, RE) allow ADUs by right.
• Lot dimensions: Measure or pull your plot map. You need to confirm there’s room for a detached ADU with 4-foot setbacks, or identify where a conversion or addition will go.
• Utility access: Identify where sewer, water, gas, and electrical connect. Distance from existing connections to the ADU location directly affects cost.
• HOA check: California law prohibits HOAs from banning ADUs, but they can impose design review. Know this upfront.
• Coastal Zone: If your property is in the California Coastal Zone (common in San Diego, parts of LA), you may need a separate Coastal Development Permit.

Many ADU builders offer free feasibility assessments. Take advantage of this — it costs nothing and identifies deal-breakers before you invest in plans. Find verified builders in Sacramento, Los Angeles, San Diego, and the SF Bay Area.

Step 2: Design and Plans (Weeks 2–6)

You need construction drawings prepared by a licensed architect or designer. These plans must include:

• Site plan showing the ADU location, setbacks, and property boundaries
• Floor plan with room dimensions, doors, windows, and fixtures
• Elevation drawings (front, sides, rear)
• Structural engineering calculations
• Title 24 energy compliance report
• Electrical, plumbing, and mechanical plans

Cost: Architectural plans typically run $4,000 to $15,000 depending on complexity. Structural engineering adds $2,500 to $8,000. Title 24 energy calculations add $1,200 to $3,000. Total soft costs for plans and engineering: $10,000 to $25,000.

Alternative: Pre-approved standard plans (available in LA, San Diego, and some other cities) skip most of the design review process. If your project fits a standard plan, permitting can be dramatically faster. More on this below.

Step 3: Submit the Application (Week 6–7)

Submit your completed plans to the local building department. The submission typically includes:

• Completed permit application form
• Three sets of construction drawings (some cities accept digital submissions)
• Structural calculations
• Title 24 energy report
• Soil report (if required — common for detached ADUs)
• Site survey
• Application fees (non-refundable)

Most cities now offer online submission through their permitting portal. Sacramento uses the SacPermits portal. Los Angeles uses LADBS Online. San Diego uses the Development Services portal. Submit digitally whenever possible — it’s faster and creates a paper trail.

Step 4: Plan Check Review (Weeks 7–15)

This is where most of the waiting happens. A plan checker reviews your drawings for code compliance. The review covers structural integrity, fire safety, energy efficiency, accessibility, and zoning compliance.

What to expect:

• First review: The plan checker issues a correction letter listing everything that needs to be revised. Almost every submission receives corrections — this is normal, not a rejection.
• Resubmission: Your architect or engineer revises the plans and resubmits. This cycle can repeat 2 to 3 times for complex projects.
• Approval: Once all corrections are resolved, the plans are approved and the permit is issued.

State law requires a decision within 60 days. In practice, the clock resets each time corrections are issued. A clean submission with no corrections can be approved in 3 to 4 weeks. A complex project with multiple rounds of corrections can take 3 to 4 months.

Step 5: Pay Fees and Pull the Permit (Week 15–16)

Once plans are approved, you pay the remaining permit fees and receive the building permit. Your contractor can now begin ADU construction. The permit must be posted visibly at the job site.

Step 6: Construction and Inspections (Months 4–12)

During construction, the building department conducts inspections at key milestones:

• Foundation inspection — before concrete is poured
• Framing inspection — after walls, roof, and structural elements are in place
• Rough plumbing, electrical, and mechanical — before walls are closed
• Insulation and energy inspection — Title 24 compliance verification
• Drywall inspection — after drywall is hung but before taping and finishing
• Final inspection — everything complete, all systems tested

Failed inspections require corrections and re-inspection. Each failed inspection adds days to weeks to the timeline. A good contractor schedules inspections proactively and addresses issues before calling the inspector. For a full breakdown of what to expect during the build phase, see our ADU construction guide.

Step 7: Certificate of Occupancy (Final Week)

After the final inspection passes, the building department issues a Certificate of Occupancy (or Certificate of Completion in some jurisdictions). This document legally authorizes the ADU for habitation. Without it, you cannot legally rent the unit, and the ADU has no assessed value for property tax purposes.

This trips up more homeowners than almost any other issue. The building department that reviews your ADU permit depends on whether your property is within a city’s limits or in unincorporated county territory.

Region	City Jurisdiction	County Jurisdiction
Sacramento	City of Sacramento Community Development	Sacramento County Planning
Los Angeles	LADBS (LA Dept of Building & Safety)	LA County Dept of Public Works
San Diego	SD Development Services Dept	SD County Planning & Development

How to check: Look at your property tax bill. It will list the jurisdiction. You can also search your address on your county assessor’s website. If you’re in an incorporated city, the city handles your permit. If you’re in unincorporated territory, the county handles it.

This matters because city and county processes, fees, and timelines are different. A contractor experienced in City of San Diego permitting may not be familiar with San Diego County’s process — and vice versa. Ask your builder which jurisdiction they’ve permitted in.

Permit fees vary dramatically by jurisdiction. Here’s what homeowners are paying in California’s three largest ADU markets:

Fee Category	Sacramento	Los Angeles	San Diego
Building permit	$1,000–$3,500	$1,500–$5,000	$1,200–$4,000
Plan check	$650–$2,300	$1,000–$3,500	$800–$2,500
School fees	$1,500–$5,000	$2,000–$6,000	$1,500–$5,000
Sewer connection	$2,000–$5,000	$3,000–$8,000	$2,000–$5,000
Impact fees (>750 sq ft)	$0–$3,000	$0–$4,000	$0–$3,000
Total permit costs	$3,000–$12,000	$4,000–$15,000	$3,000–$12,000

Fee waiver: Under California law, ADUs under 750 sq ft are exempt from most development impact fees. This can save $2,000 to $4,000 depending on jurisdiction. If your ADU is near the 750 sq ft threshold, designing it just under that limit can result in meaningful fee savings.

For complete cost breakdowns by city, see our cost guides for Sacramento, Los Angeles, and San Diego.

State law says 60 days. Reality says otherwise. Here’s what homeowners actually experience:

City	Typical Timeline	Standard Plan	Notes
Sacramento	4–8 weeks	2–4 weeks	Generally efficient; online submission available
Los Angeles	8–16 weeks	3–6 weeks	Highest volume; correction cycles are common
San Diego	4–8 weeks	2–3 weeks	Fastest major city; strong standard plan program

Why LA takes longer: LADBS processes more ADU permits than any other building department in the country. The sheer volume creates backlogs. Plan check corrections are more common because LADBS has stricter interpretations of certain code provisions, particularly around hillside construction, fire zones, and historic preservation overlay zones.

What you can control: The single biggest factor in permit timeline is the quality of your initial submission. A clean, complete submission with no errors can be approved on the first review cycle. A sloppy submission with missing calculations or non-compliant setbacks triggers corrections that add weeks or months. This is where having an architect and engineer who know your specific city’s requirements matters.

California’s ADU laws have been updated multiple times since 2017. Here are the bills that matter most in 2026:

AB 68 / SB 13 / AB 881 (2020) — The Foundation

These three bills collectively eliminated most local barriers to ADU construction. They established the 60-day approval requirement, removed parking mandates, reduced setbacks to 4 feet, and prohibited cities from imposing minimum lot sizes for ADU eligibility. This is the legal framework that made California’s ADU boom possible.

SB 9 (2022) — Lot Splits and Duplexes

SB 9 allows homeowners to split a single-family lot into two parcels and build up to two units on each parcel — potentially four units where one house stood. This is separate from ADU law but can be combined with it. On a lot split under SB 9, each new parcel can also have an ADU. The interaction between SB 9 and ADU law varies by city, so consult your local building department for specifics.

AB 976 (2024) — Permanent ADU Owner-Occupancy Removal

AB 976 permanently eliminated the owner-occupancy requirement for standard ADUs. Before this bill, the removal of owner-occupancy was temporary and set to expire. Now it’s permanent California law. You do not need to live on the property to build or rent an ADU. The exception: JADUs may still require owner-occupancy under certain conditions.

SB 543 (2025–2026) — Permit Processing Reforms

SB 543 is the most recent significant ADU law. It strengthens the 60-day approval mandate by requiring cities to issue a completeness determination within 15 days of submission and provide itemized deficiency lists if corrections are needed. It also introduces appeal rights for homeowners whose ADU applications are denied. For a full breakdown, read our California ADU Law Explained (SB 543) guide.

Permit rejections are usually avoidable. Here are the most common reasons California ADU applications fail:

1. Setback violations. Detached ADUs require 4-foot rear and side setbacks. Attached ADUs must meet the primary structure’s setback requirements. Measuring from the wrong reference point (property line vs. easement line vs. fence) is the most common error.

2. Height exceeding limits. Detached ADUs are limited to 16 feet for single-story or 18 feet if within half a mile of transit. Two-story ADUs may be allowed up to 18–25 feet under AB 976, but this varies by jurisdiction. Exceeding the height limit by even a few inches triggers a correction.

3. Incomplete structural calculations. Missing or incorrect structural engineering is the top reason for plan check corrections. Foundation design, lateral load analysis, and connection details must be complete and stamped by a licensed structural engineer.

4. Title 24 non-compliance. California’s energy code (Title 24) requires specific insulation values, window performance ratings, and HVAC efficiency levels. Submitting plans without a compliant Title 24 energy report guarantees a correction.

5. Sewer capacity issues. Some jurisdictions require a sewer capacity study or lateral inspection before approving an ADU. In older neighborhoods with aging sewer infrastructure, the city may require lateral replacement as a condition of the permit.

6. Fire department issues. Properties in Very High Fire Hazard Severity Zones (VHFHSZ) face additional requirements: fire-resistive roofing, ember-resistant vents, tempered glass windows, and brush clearance. Missing any of these triggers a fire department correction.

7. Incomplete application. Missing documents, unsigned forms, or insufficient copies. This sounds basic, but it accounts for a significant percentage of first-round rejections. Use the building department’s submittal checklist.

Several California cities offer pre-approved ADU designs that skip most of the plan check process. If your project fits a standard plan, permitting can take as little as 2 weeks instead of 2 months.

• Los Angeles (LADBS): Offers a Standard Plan Program with multiple pre-approved ADU designs. Qualifying projects go through an expedited review.
• San Diego: Has pre-approved several prefab and site-built ADU designs. The city actively promotes standard plans to reduce permit review times.
• Sacramento: Accepts state-compliant pre-approved plans and offers expedited review for qualifying designs.

Limitations: Standard plans work best for flat lots with straightforward utility connections. If your lot has slope, unusual soil conditions, easements, or non-standard setback requirements, a standard plan may not fit and you’ll need custom plans.

Ask your builder whether they have experience with standard plans in your city. Some ADU companies — particularly prefab builders — have their own pre-approved designs on file with specific building departments.

Do I need a permit to build an ADU in California?

Yes. All ADU construction in California requires a building permit from the local building department. This includes detached ADUs, attached ADUs, garage conversions, and JADUs. Building without a permit is illegal, and unpermitted ADUs cannot be legally rented, insured, or included in a property appraisal.

How long does it take to get an ADU permit in California?

California law requires cities to approve or deny a complete ADU application within 60 days. In practice, permitting takes 4 to 8 weeks in Sacramento and San Diego, and 8 to 16 weeks in Los Angeles. Projects using pre-approved standard plans can be permitted in as little as 2 weeks.

How much does an ADU permit cost in California?

Total ADU permit costs range from $3,000 to $15,000 depending on the city and ADU size. This includes building permit, plan check, school fees, sewer connection, and any applicable impact fees. ADUs under 750 sq ft are exempt from most development impact fees under California law.

Can a city deny my ADU permit in California?

A city can deny an ADU permit if the application doesn’t meet building code, zoning requirements, or state ADU law. However, cities cannot impose restrictions beyond what state law allows — such as minimum lot sizes, parking requirements, or owner-occupancy mandates for standard ADUs. SB 543 gives homeowners appeal rights if they believe a denial is unjustified.

Do I need an architect to get an ADU permit?

California does not require a licensed architect for ADU plans in all cases, but most building departments require construction drawings prepared by a licensed design professional (architect or licensed designer) for structural work. A structural engineer is required for foundation and framing calculations. In practice, hiring both an architect and structural engineer is standard for ADU projects.

Can I get an ADU permit without a contractor?

You can pull an owner-builder permit and act as your own general contractor. However, you must still submit professionally prepared plans, pass all inspections, and comply with all building codes. Most homeowners hire a licensed general contractor because the complexity of ADU construction — foundation, structural, plumbing, electrical, HVAC — exceeds typical DIY capability.

What happens if I build an ADU without a permit?

Building without a permit is a code violation that can result in fines, stop-work orders, mandatory demolition, inability to sell the property, and personal liability if someone is injured in the unpermitted structure. Unpermitted ADUs also cannot be legally rented and are not covered by homeowner’s insurance.

Does the CalHFA grant cover permit fees?

Yes. The CalHFA ADU grant of up to $40,000 covers pre-development costs including permit fees, plan check fees, impact fees, architectural plans, engineering, and site surveys. It does not cover construction costs. Read our CalHFA ADU Grant guide for full eligibility details.

How much does an ADU permit cost in Sacramento?

ADU permit costs in Sacramento typically run $3,000 to $8,000 total. The city charges lower impact fees than LA or the Bay Area, and ADUs under 750 sq ft are exempt from most development impact fees. Plan check and building permit fees scale with project valuation. Sewer and water connection fees vary by distance from existing service lines.

Can I get an ADU permit for a garage conversion?

Yes. Garage conversions are one of the fastest ADU types to permit in California because the structure already exists. You still need a building permit for the conversion — it involves changing the occupancy classification from storage to habitable space, which triggers requirements for insulation, egress windows, plumbing, electrical, and fire separation. Most cities process garage conversion permits faster than new construction because the structural review is simpler. For cost details, see our garage conversion cost guide.

Do ADU permits expire in California?

Yes. Building permits in California are typically valid for 12 months from the date of issuance. If construction has not started or if no inspection has occurred within that window, the permit expires and you must reapply. Some cities offer permit extensions — typically 6 months — if you request one before expiration. Once a permit expires, any fees paid are generally not refundable.