Permit Process for ADUs in California: Step-by-Step + Costs
Building an Accessory Dwelling Unit (ADU) is an excellent way to add value to your property, create rental income, or provide a separate living space for family. California has made it easier than ever for homeowners to build these secondary units. However, navigating the permit process can still feel like a significant hurdle. Understanding the steps, timelines, and costs involved is crucial for a smooth and successful project.
This guide breaks down everything you need to know about the ADU permit process in California. We will cover the specific costs you can expect, the step-by-step application process, how long it takes, and the overall construction costs in the Bay Area. With this information, you can approach your ADU project with confidence and clarity, ready to work with experienced ADU builders to bring your vision to life.
Why Do You Need a Permit for an ADU?
Before we dive into the details, it’s important to understand why permits are a non-negotiable part of building an ADU. A building permit is your local government’s official approval to proceed with a construction or remodeling project. It ensures that your ADU is safe, structurally sound, and compliant with all state and local building codes.
These codes cover everything from fire safety and electrical wiring to plumbing and energy efficiency. An unpermitted ADU can lead to significant problems, including fines, orders to demolish the structure, and difficulty selling your property in the future.
Securing a permit protects your investment, ensures the safety of its occupants, and confirms the legality of your new unit. Working with a qualified ADU contractor is the best way to ensure every aspect of your project meets these stringent requirements from day one.
How much does an ADU permit cost in California?
One of the first questions homeowners ask is about the cost. The truth is, there isn’t one single answer. The cost of an ADU permit in California varies widely depending on your location, the size of your unit, and the complexity of your project. Each city and county has its own fee schedule, so costs can range from a few thousand dollars to over ten thousand.
Here are the common fees that make up the total permit cost:
- Plan Check Fees: Before a permit is issued, the local building department must review your architectural plans to ensure they comply with building codes. This fee covers the time and expertise required for that review. It is often calculated based on the project’s valuation or the square footage of the proposed ADU.
- Building Permit Fees: This is the primary fee for the permit itself. It’s typically based on the estimated cost of construction. The higher the project valuation, the higher the permit fee.
- School Impact Fees: In some jurisdictions, new residential units, including ADUs, are subject to fees that help fund local schools. However, thanks to recent state laws, ADUs under 750 square feet are exempt from these fees. For larger ADUs, the fee is calculated on a per-square-foot basis.
- Utility Connection Fees: If your ADU requires a new connection for water, sewer, or electricity, you will likely have to pay connection fees. For ADUs created within an existing structure (like a garage conversion), you may be able to avoid new connections. For new detached ADUs, these fees are more common but are often prorated based on the size of the unit relative to the primary home.
- Other Miscellaneous Fees: Depending on your location, you might also encounter fees for planning department review, public works inspection, or even park fees.
To get an accurate estimate, you should contact your local city or county planning department. They can provide a detailed fee schedule. An experienced ADU contractor or design-build firm will also be able to give you a very close estimate of these costs as part of their initial project assessment. While permit fees can seem substantial, they are a critical investment in the long-term value and safety of your property.
How to get a permit for an ADU in California?
Getting a permit for an ADU in California involves a series of structured steps. While the specifics can vary slightly between jurisdictions, the general process remains consistent. Here is a step-by-step guide to help you navigate the journey.
Step 1: Research and Due Diligence
Before you even think about drawing up plans, start with research. Your first stop should be your local city or county planning department’s website. Look for their ADU-specific guidelines. Key information to find includes:
- Zoning Requirements: Is your property zoned for an ADU? Most residential lots are, but it’s essential to confirm.
- Setback Requirements: How far must the ADU be from your property lines and the main house?
- Size Limitations: What is the maximum and minimum size allowed for an ADU on your lot?
- Parking Rules: California state law prohibits local governments from requiring a replacement parking spot for a garage conversion. For other ADUs, a parking spot might be required unless your property is located near public transit.
- Owner-Occupancy Rules: State law has also suspended local owner-occupancy requirements until 2025, making it easier for investors.
This initial research will tell you what is feasible on your property and will inform the design of your ADU.
Step 2: Hire Your Professional Team
An ADU project is not a simple DIY task. You will need a team of professionals to create the necessary plans and documents for your permit application. This team typically includes:
- An Architect or Designer: They will create the detailed architectural plans for your ADU, including floor plans, elevations, and structural details.
- A Structural Engineer: An engineer will be needed to calculate structural loads and design the foundation and framing to ensure the building is stable and safe.
- An ADU Contractor or Builder: Engaging reputable ADU builders early in the process is highly beneficial. They can provide valuable input on construction costs, material choices, and potential challenges. Their practical experience can help refine the design to stay within your budget.
Choosing an experienced team is the most important decision you will make. Look for professionals with a proven track record of successfully permitted and built ADUs in your area.
Step 3: Develop Your Plans
With your team in place, you will work with your architect or designer to create a complete set of construction documents. This package is much more than just a floor plan. It typically includes:
- Site Plan: Shows the entire property, including the location of the main house, the proposed ADU, property lines, and any other structures.
- Architectural Plans: Detailed floor plans, roof plans, exterior elevations, and building sections.
- Structural Plans: Foundation design, framing plans, and structural calculations from the engineer.
- Title 24 Energy Calculations: A report showing the ADU complies with California’s energy efficiency standards.
- Supporting Documents: This may include a soils report, a survey, or other documents required by your local jurisdiction.
This phase requires careful coordination between you and your design team to ensure the final plans reflect your vision while meeting all code requirements.
Step 4: Submit Your Application
Once your plan set is complete, it’s time to submit it to your local building department. Most cities now use a digital submission portal, which streamlines the process. You will need to fill out the permit application forms, upload all your documents, and pay the initial plan check fees.
After submission, your application will enter the queue for review. A plan checker will be assigned to your project and will meticulously review every detail of your plans to ensure they are compliant with local and state codes.
Step 5: Respond to Comments and Revisions
It is very common for the building department to return your plans with comments or required corrections. This is a normal part of the process and does not mean your project is rejected. Your architect or engineer will review the comments, make the necessary revisions to the plans, and resubmit them.
This back-and-forth can sometimes happen more than once. The key is to respond to the comments promptly and thoroughly. A good ADU contractor or designer will have experience with the specific requirements of your local department and can often anticipate and address potential issues in the initial design, minimizing the number of revision cycles.
Step 6: Permit Issuance
Once the plan checker is satisfied that all codes have been met, they will approve your plans. You will be notified that your permit is ready to be issued. At this point, you will pay the remaining permit fees, and the building department will issue your official ADU building permit.
With the permit in hand, your ADU builders can finally break ground and begin construction. The permit must be posted visibly at the construction site throughout the project.
How long does it take to get an ADU permit in California?
Under California state law, local agencies must approve or deny an ADU permit application within 60 days of receiving a complete submission. This law was put in place to streamline the process and prevent lengthy delays that previously plagued ADU projects.
However, the “60-day clock” only starts once the building department deems your application “complete.” If your initial submission is missing documents or has significant errors, the clock doesn’t start. Furthermore, if the department requests revisions, the clock pauses until you have resubmitted the corrected plans.
Realistically, you should plan for the entire permit process—from starting the design to having the permit in hand—to take anywhere from three to six months. Here’s a typical breakdown:
- Design and Plan Development: 1-2 months
- Initial Plan Review by the City: 1-2 months
- Revisions and Resubmission: 2-4 weeks
- Final Approval and Permit Issuance: 1-2 weeks
The timeline can be influenced by the complexity of your project, the workload of your local building department, and the experience of your design team. Working with professionals who are familiar with your local jurisdiction’s process can significantly speed things up.
How Much Does It Cost To Build an ADU in the Bay Area?
While permit fees are an important part of the budget, the primary expense is the construction itself. The cost to build an ADU in the San Francisco Bay Area is among the highest in the nation due to high labor costs, material prices, and the region’s strong economy.
As of 2026, homeowners in the Bay Area can expect construction costs to range from $400 to over $700 per square foot. This wide range depends on several factors:
- Type of ADU: A garage conversion is typically the most affordable option, as the foundation and structure are already in place. A detached, new-construction ADU will be the most expensive. An ADU built above a garage falls somewhere in the middle.
- Size: While a larger ADU will have a higher total cost, the cost per square foot often decreases slightly as the size increases due to economies of scale.
- Level of Finishes: The choices you make for flooring, countertops, cabinets, fixtures, and appliances will have a major impact on the final cost. Basic, builder-grade finishes will keep costs down, while high-end, custom selections will increase the budget significantly.
- Site Conditions: A flat, easily accessible lot will be cheaper to build on than a sloped lot that requires extensive grading, retaining walls, or a complex foundation.
- Utility Connections: The distance from the ADU to the main utility hookups for sewer, water, and electricity can also affect the cost. Longer trenching distances mean higher labor and material costs.
For a typical 500-square-foot detached ADU in the Bay Area, you can expect the total project cost—including design, permits, and construction—to be anywhere from $250,000 to $400,000 or more. A garage conversion might range from $120,000 to $200,000.
Because of this significant investment, it is vital to work with a trusted and transparent ADU builder. A reputable firm will provide a detailed breakdown of all anticipated costs, helping you make informed decisions and avoid unexpected expenses down the road.
Your Trusted ADU Builder in the Bay Area
The permit process for an ADU in California is detailed and requires careful attention, but it is entirely manageable with the right team. By understanding the costs, steps, and timelines involved, you can plan effectively and set your project up for success.
At Bayside Builders Group, we specialize in helping homeowners navigate every stage of the ADU journey. From initial design and permit acquisition to full construction, our experienced team is committed to making the process as smooth and transparent as possible. We are the ADU contractor you can trust to deliver a high-quality unit on time and on budget.
If you’re ready to explore the potential of an ADU on your property, contact us today. We can help you understand the specific requirements in your area and provide a clear path forward to achieving your goals.
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ADU Permit & Construction FAQs
Do I really need a permit to build an ADU in California?
Yes, a building permit is legally required for any ADU construction. This ensures your unit is safe, meets all state and local building codes, and protects your property’s value. Building without a permit can lead to fines and legal issues.
How much does an ADU permit cost in California?
he cost varies by location but typically ranges from a few thousand to over ten thousand dollars. This total includes plan check fees, building permit fees, and potentially school impact and utility connection fees, depending on your ADU’s size and city regulations.
How long does it take to get an ADU permit approved?
While state law requires local agencies to act within 60 days of a complete application, the entire process from design to permit issuance usually takes three to six months. This timeline accounts for plan development, city review, and any necessary revisions.
What is the first step to getting an ADU permit?
The first step is research. Before hiring anyone, check your local city or county planning department’s website for specific ADU rules regarding zoning, size limits, and setback requirements for your property.
Who do I need to hire for my ADU project?
You will need a professional team, which typically includes an architect or designer to create the plans and a structural engineer for safety and stability calculations. Engaging an experienced ADU contractor early in the process is also crucial for budgeting and design feedback.
What happens if the city requests revisions to my plans?
This is a very common part of the process. Your architect or engineer will review the city’s comments, update the plans accordingly, and resubmit them. Working with experienced ADU builders can help minimize these revisions by anticipating local requirements.
What is the average cost to build an ADU in the Bay Area?
Construction costs in the Bay Area generally range from $400 to over $700 per square foot. The final cost depends on the type of ADU, its size, site conditions, and the quality of finishes you choose.
Is a garage conversion cheaper than building a new ADU?
Yes, converting an existing garage is typically the most cost-effective option. You can save significantly since the foundation, walls, and roof structure are already in place. A new, detached ADU is the most expensive type.
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