How Long Does ADU Plan Check Really Take in California?

The Reality of ADU Plan Check Timelines in California

If there is one aspect of the ADU permitting process that frustrates homeowners more than any other, it is plan check. The time between submitting your construction plans and receiving approval to begin building can stretch from weeks to months, depending on your jurisdiction, the quality of your plans, and the current workload of the building department.

California law (Government Code Section 65852.2) requires local agencies to act on ADU applications within 60 days of receiving a complete application. However, the key phrase is "complete application," and many submissions are returned as incomplete, resetting the clock. In practice, the total time from first submission to permit issuance is often significantly longer than 60 days.

This guide provides realistic plan check timelines based on actual homeowner and contractor experiences across California, explains what factors affect review duration, and offers proven strategies to minimize delays and get your ADU project approved as quickly as possible.

Plan Check Timelines by California City

Plan check timelines vary dramatically across California. Some cities have streamlined their ADU review process, while others are overwhelmed with applications and have significant backlogs. Here are real-world timelines as of 2026:

These timelines represent the plan check phase only. The total time from concept to permit includes design (4 to 8 weeks), engineering and report preparation (2 to 4 weeks), plan check (above), and corrections/re-review (2 to 6 weeks). For many homeowners, the total pre-construction phase takes 4 to 8 months.

What Happens During Plan Check

Understanding what plan checkers are actually reviewing helps explain why the process takes as long as it does. A typical ADU plan check involves review by multiple departments and disciplines:

Building Code Review

The primary plan checker reviews your plans for compliance with the California Building Code (CBC), including structural adequacy, fire safety, egress requirements, room dimensions, ceiling heights, and accessibility. This is the most comprehensive review and typically takes the longest.

Fire Department Review

The fire department reviews fire access, fire sprinkler requirements (if applicable), smoke detector placement, and fire-rated assemblies. ADUs over 150 feet from a fire hydrant or in high fire hazard severity zones may face additional requirements.

Planning/Zoning Review

The planning department verifies that your ADU complies with zoning regulations, including setbacks, height limits, lot coverage, and parking requirements. This review also checks for any overlay zone requirements (HPOZ, specific plan areas, etc.).

Mechanical, Electrical, and Plumbing Review

Separate reviewers (or the primary plan checker) verify that HVAC, electrical, and plumbing plans comply with the relevant codes (Mechanical Code, Electrical Code, Plumbing Code).

Grading and Drainage Review

The public works or engineering department reviews grading and drainage plans for compliance with local stormwater requirements and LID (Low Impact Development) standards.

Energy and Green Building Review

A reviewer verifies Title 24 energy compliance documentation and CALGreen building code compliance.

What Causes Plan Check Delays

1. Incomplete Submissions

The single most common cause of plan check delays is an incomplete submission. If your application is missing required documents, calculations, or fees, the building department will return it as incomplete, and the 60-day clock does not start until you resubmit with all required materials.

Common items that cause incompleteness:

• Missing Title 24 energy calculations
• Incomplete structural calculations or engineering
• Missing geotechnical (soils) report
• Incomplete or missing drainage plan
• Missing property survey or inaccurate site plan
• Incorrect or missing fee payment

2. Plan Corrections

Even complete submissions often receive correction comments from plan checkers. Each round of corrections requires you to revise and resubmit your plans, adding 2 to 6 weeks per cycle. First-time ADU plan submissions average 1 to 3 rounds of corrections before approval. Experienced ADU architects and designers who submit regularly to the same jurisdiction average 0 to 1 rounds of corrections.

3. Multiple Department Reviews

When reviews are conducted sequentially (building, fire, planning, engineering), the total time is the sum of each review. Some jurisdictions conduct concurrent reviews (all departments review simultaneously), which is much faster. Ask your building department whether reviews are sequential or concurrent.

4. Staffing Shortages

Many California building departments are understaffed due to budget constraints and difficulty recruiting qualified plan checkers. The surge in ADU applications since 2020 has overwhelmed some departments, creating backlogs that extend review times well beyond the 60-day statutory limit.

5. Complex Site Conditions

Properties in hillside zones, flood zones, fire hazard zones, or historic overlay areas require additional reviews and approvals that can significantly extend the timeline. These properties may need discretionary review in addition to the standard plan check, which adds months to the process.

Proven Strategies to Speed Up Plan Check

1. Use Pre-Approved Plans

Several California cities now offer pre-approved ADU plans that have already passed plan check. If you use a pre-approved plan, the review focuses only on site-specific conditions (setbacks, utility connections, grading) rather than reviewing the entire building design from scratch. This can reduce plan check time by 50% to 75%.

Cities offering pre-approved ADU plans include San Jose, Sacramento, Los Angeles, and several smaller jurisdictions. Check with your local building department for available options.

2. Hire an Experienced ADU Architect/Designer

An architect or designer who regularly submits ADU plans to your specific building department knows exactly what the plan checkers expect. Their submissions are less likely to receive corrections, and when corrections do come, they know how to respond quickly and accurately.

Ask potential architects how many ADU plans they have submitted to your specific city and what their typical correction rate is. An experienced ADU architect should have a correction rate of less than one round per submission.

3. Pre-Application Meeting

Many building departments offer pre-application meetings where you can discuss your project with a plan checker before submitting full plans. This meeting can identify potential issues early, allowing you to address them in your initial submission rather than during corrections.

4. Express Plan Check

Some jurisdictions offer expedited or express plan check for an additional fee. In Los Angeles, LADBS offers an express plan check service that can reduce review time by 30% to 50%. The additional fee is typically 50% to 100% of the standard plan check fee, but the time savings can be worth it if your project timeline is critical.

5. Submit Complete, Accurate Plans

This seems obvious but is the most effective strategy. A complete submission with no errors bypasses the most common delays. Before submitting, verify that your package includes every required document, that all calculations are complete and accurate, and that the plans address every applicable code section.

Create a submission checklist based on your building department's published requirements. Many departments post detailed checklists on their websites. Review every item before submitting.

Navigating the Correction Process

When plan check corrections are issued, efficiency in responding is critical. Each round of corrections adds 2 to 6 weeks to the timeline (submission queue time plus re-review time). Here is how to handle corrections effectively:

1. Review all comments carefully: Read every correction comment thoroughly before starting revisions. Some comments are interconnected, and addressing one may resolve others.
2. Respond to every comment: Provide a written response to each correction, even if the response is "See revised sheet A-2." Building departments require documented responses to each comment.
3. Call the plan checker for clarification: If any comment is unclear, call the plan checker before revising. It is better to spend 10 minutes on the phone than to misinterpret a comment and trigger another round of corrections.
4. Mark revisions clearly: Use revision clouds, delta symbols, or highlighting to indicate where changes were made on the revised plans. This helps the plan checker find your revisions quickly, speeding up the re-review.
5. Submit corrections promptly: Every day of delay on your end adds to the total timeline. Aim to resubmit within 5 to 10 business days of receiving corrections.

Your Rights Under California Law

California law provides several protections for ADU applicants that are worth knowing:

• 60-day mandate: Local agencies must approve or deny a complete ADU application within 60 days. If no action is taken, the application is deemed approved by operation of law.
• No discretionary review: ADU applications that meet objective standards are subject to ministerial (non-discretionary) review only. Building departments cannot impose subjective design standards or require public hearings for code-compliant ADU applications.
• HCD oversight: The California Department of Housing and Community Development (HCD) monitors local jurisdictions for compliance with ADU law. If you believe your building department is not processing your application in compliance with state law, you can file a complaint with HCD.
• Completeness determination: Building departments must provide a written determination of completeness within 30 days of receiving your application. If they fail to do so, the application is deemed complete.

Plan Check Is a Marathon, Not a Sprint

ADU plan check in California is a process that rewards preparation, patience, and persistence. The homeowners who navigate it most successfully are those who invest in quality plans, hire experienced professionals, submit complete applications, and respond to corrections quickly and thoroughly.

While the timeline can be frustrating, remember that plan check serves an important purpose: ensuring that your ADU is designed and will be built to current safety and building code standards. A thorough plan check protects you, your future tenants, and your investment.

If you are concerned about plan check timelines in your jurisdiction, start the design and engineering process as early as possible. The time spent getting your plans right before submission is almost always repaid in a faster, smoother plan check with fewer corrections.

Tips for Expediting Your ADU Plan Check in California

If time is a priority for your ADU project, several strategies can help move your application through plan check faster.

Submit Complete and Accurate Plans

The single most effective way to speed up plan check is to submit a thorough, complete plan set on the first attempt. Incomplete submittals are the leading cause of delays. Ensure your plans include all required sheets, calculations, and compliance forms. Use the pre-submission checklist to verify every item before submitting.

Use Pre-Approved ADU Plans

Many California cities now offer pre-approved ADU plan libraries. These standardized designs have already been reviewed for code compliance, which can reduce plan check time from weeks to days. Los Angeles, San Jose, San Diego, and Sacramento are among the cities with active pre-approved plan programs. While pre-approved plans limit customization, they offer a significant time advantage for homeowners who prioritize speed.

Hire an Experienced ADU Designer

Architects and designers who specialize in ADU projects understand the specific requirements and common pitfalls that trigger plan check corrections. Their familiarity with local code interpretations and submittal preferences can reduce the number of correction rounds. Ask potential designers how many ADU projects they have completed in your specific jurisdiction and what their typical first-round approval rate is.

Consider Third-Party Plan Review

Some California jurisdictions allow or require third-party plan review for certain project types. Private plan check firms often have shorter turnaround times than municipal building departments because they are not subject to the same staffing constraints. However, third-party review typically costs $2,000 to $5,000 on top of regular permit fees. Weigh this cost against the value of getting your ADU project started sooner.

Respond to Corrections Promptly and Completely

When you receive plan check corrections, respond to every item in a single resubmittal. Partial responses that address only some corrections will be sent back for additional review, adding another full review cycle to your timeline. Mark each correction on your plans, include a written response sheet that references each comment by number, and have your designer verify all corrections before resubmitting.

When to Use Expedited Plan Check Review

Several California cities offer expedited or fast-track plan check services for ADU applications. Here is when this option makes financial sense:

• Time-sensitive projects. If you have a construction crew scheduled or a seasonal deadline, expedited review can save 2 to 6 weeks compared to standard processing.
• Rental income urgency. If your ADU is intended for rental income, every month of delay costs you potential revenue. An expedited review fee of $1,000 to $3,000 may be worthwhile if your expected monthly rent is $2,000 or more.
• Construction loan carrying costs. If you are financing your ADU with a construction loan, you are paying interest on borrowed funds during the plan check period. Faster approval means lower total financing costs.
• Simple, straightforward projects. Expedited review works best for uncomplicated ADU designs that are unlikely to require multiple correction rounds. Complex projects with engineering challenges may not benefit from expedited processing since corrections will still require full review cycles.

Frequently Asked Questions About ADU Plan Check Timelines

Can I start any construction work while my plans are still in plan check?

No. California law prohibits any construction work without an approved building permit. Beginning construction before permit issuance can result in stop-work orders, fines, and potentially having to demolish unpermitted work. However, you can use the plan check period productively by finalizing material selections, scheduling subcontractors, and coordinating site preparation logistics.

Why do some cities process ADU plan checks faster than others?

Processing times vary based on staffing levels, application volume, local code complexity, and departmental efficiency. Cities that have invested in dedicated ADU plan check teams or streamlined online submission portals tend to process applications faster. Cities experiencing high construction volume or staffing shortages may have longer backlogs. Contact your local building department to ask about current average processing times before submitting.

Does the type of ADU affect plan check duration?

Yes, generally simpler ADU types are reviewed faster. A garage conversion or Junior ADU (JADU) typically has a shorter plan check than a new detached ADU because there is less structural engineering to review. Two-story ADUs often take longer than single-story designs due to additional structural, fire safety, and setback requirements. Properties in hillside, flood zone, or fire hazard areas may also trigger additional review from specialized departments.

What happens if my plan check expires before I address all corrections?

Most California jurisdictions give applicants 6 to 12 months to respond to plan check corrections. If your application expires, you may need to resubmit and pay new plan check fees. Some cities allow extensions if you request them before the deadline. Keep track of your application timeline and respond to corrections well before any expiration date to avoid losing your place in the review queue.

Can I track the status of my ADU plan check online?

Many California building departments now offer online permit tracking systems where you can monitor the status of your application. Los Angeles, for example, provides online status updates through its building department portal. If your city does not offer online tracking, call the building department counter to check on your application status. Having your permit application number readily available will expedite any status inquiry.