Navigating San Diego County ADU Plans: A How-To Guide


When you are considering San Diego County ADU plans, the process can feel overwhelming. With varied rules and design options, it can be tough to know where to start. But don’t worry, we’ve got you covered right here.

ADU Key Points:
1. Building Permit Required: All ADUs need a building permit.
2. Maximum Sizes: Generally, up to 1,200 sq.ft. for detached ADUs.
3. Pre-Approved Plans Available: Faster permitting with county-owned designs.

Accessory Dwelling Units (ADUs) are additional living spaces built on the same lot as your primary home. They can serve as rental homes, housing for family, or guest suites. In San Diego County, ADUs are an excellent way to maximize your property value and address housing needs. Understanding local regulations and leveraging pre-approved plans can simplify this complex process.


Summary of San Diego County ADU Key Points - san diego county adu plans infographic process-5-steps-informal

Understanding San Diego County ADU Regulations

Zoning Requirements

In San Diego County, zoning regulations determine where you can build an ADU. These rules vary based on whether your property is zoned for single-family or multifamily use.

Single-Family Zones: You can add one ADU and one Junior ADU (JADU) to lots with an existing or proposed single-family home.

Multifamily Zones: You can have multiple ADUs, often up to 25% of the existing units.

Lot Size: While there’s no minimum lot size, the size of your ADU is often limited by your lot’s size and zoning.

Residential Zones: ADUs are allowed in most residential zones, but always check your specific zoning requirements here.

Building Codes and Safety Regulations

Building an ADU means meeting strict health and safety codes. These include:

  • Construction Standards: Your ADU must comply with local and state construction codes. This ensures the structure is safe and durable.
  • Inspections: Regular inspections are required throughout the building process to ensure compliance with all safety standards.

Pro Tip: Obtain your building permit early to avoid delays. You can apply online for minor residential permits, including window replacements and solar PV systems here.

Size Limits and Types of ADUs

Detached ADU: A standalone unit on the same lot as the main house. In San Diego County, the maximum allowed size is 1,200 sq. ft.

Attached ADU: This unit is attached to the main home. The size is usually capped at 50% of the existing home’s square footage, up to a maximum of 1,200 sq. ft.

Junior ADU (JADU): A smaller unit within the walls of the main home, typically up to 500 sq. ft.

Size Limits by Home Size:

Square Footage of Existing Home Max Detached ADU Size Max Attached ADU Size
500 sq. ft. 1,200 sq. ft. 850 sq. ft.
1,000 sq. ft. 1,200 sq. ft. 850 sq. ft.
1,800 sq. ft. 1,200 sq. ft. 900 sq. ft.
2,000 sq. ft. 1,200 sq. ft. 1,000 sq. ft.
2,200 sq. ft. 1,200 sq. ft. 1,100 sq. ft.
3,000 sq. ft. 1,200 sq. ft. 1,200 sq. ft.
4,500 sq. ft. 1,200 sq. ft. 1,200 sq. ft.

Key Point: Always check the specific size limits for your property to ensure compliance.

Permit Requirements

Building Permit: Required for all ADUs to ensure they meet zoning, building, health, and safety codes.

Plan Check Fees: Waived for qualifying projects started before January 9, 2024. However, permits must be issued before this date to benefit from the waiver.

Inspections: Regular inspections are mandatory to ensure your ADU meets all safety and building standards.

Pro Tip: Use pre-approved plans to expedite the permitting process. These plans are reviewed and approved by building authorities, saving you time and money.

ADU Building Plans - san diego county adu plans

Understanding these regulations is crucial for a smooth ADU project.

Cost and Financing Options for ADUs

Typical Construction Costs

Building an ADU in San Diego County can vary significantly in cost. On average, you can expect to pay between $300 to $500 per square foot. This wide range depends on factors such as:

  • Size of the ADU: Larger units generally cost more.
  • Fit and Finish: High-end materials and finishes will increase costs.
  • Site Conditions: Flat lots are cheaper to build on compared to sloped lots.

Example: A 600 sq.ft. ADU might cost between $180,000 and $300,000. This includes site work, construction, permitting, solar panel installation, and any site-specific requirements.

Financing Programs and Grants

Financing your ADU project can be challenging, but there are several options available:

San Diego Housing Commission’s ADU Finance Program

The San Diego Housing Commission (SDHC) offers a program that provides financial and technical assistance to low-income homeowners. This includes:

  • Construction Loans: Low-interest loans to cover building costs.
  • Technical Assistance: Help with understanding and completing the ADU building process.

Pro Tip: Check out the SDHC ADU Finance Program for more details.

Construction-to-Permanent Loans

These loans cover the construction phase and then convert into a permanent mortgage. They often come with lower interest rates and are tailored for building new structures.

Single Closing: Saves time and money.
Fixed Rates: Predictable payments.

Grants and Other Financial Assistance

While grants are less common, some programs offer financial assistance to encourage ADU development. For example, development fees for granny flats have been waived in San Diego, saving you thousands.

Additional Costs to Consider:
Sewer Connection Fees: $2,000 to $4,000.
School Fees: $2,000 to $5,000 based on square footage.
Site Work: Costs can escalate if your lot has specific challenges like slopes or insufficient access.

Understanding these costs and financing options will help you plan your ADU project effectively. Next, we’ll explore the benefits of using pre-approved ADU plans in San Diego County.

Pre-Approved ADU Plans in San Diego County

Benefits of Pre-Approved Plans

Choosing pre-approved ADU plans can simplify your project in many ways. These plans are also known as permit-ready plans, and they have already been reviewed and approved by building authorities. This means fewer changes and a faster permitting process.

Time Savings: Pre-approved plans undergo fewer revisions, which translates to quicker permit approvals. This can save you months of waiting compared to custom designs.

Cost Efficiency: Since these plans are already designed and reviewed, you save on initial design costs. Plus, the expedited permitting process can save you money on holding costs and potential delays.

Compliance with Regulations: Pre-approved plans are crafted to meet local building codes and safety regulations. This ensures your ADU is compliant from the start, reducing the risk of costly modifications later.

Plan Check Fees: While the plans themselves are free, you will need to pay for the plan check fees during the permitting process. However, these fees are generally lower because the plans are pre-approved.

Expedited Permitting: One of the biggest advantages is the expedited permitting process. Since the plans are pre-approved, the time taken for plan review is significantly reduced, allowing you to start construction sooner.

By opting for pre-approved ADU plans, you can streamline your project, save on costs, and ensure compliance with San Diego County regulations. Next, we’ll walk you through the steps to obtain a building permit for your ADU.

Steps to Obtain a Building Permit for Your ADU

Application Process

1. Submission: Start by preparing your application. This includes your plot plan, construction drawings, and any additional required documents. Submit these to the San Diego County planning department. You can do this online, which is especially helpful given the current backlog in permit applications.

2. Review: Once submitted, your application will go through a review process. This involves checking for compliance with zoning, building codes, and health & safety regulations. Be prepared for this step to take several weeks or even months due to high demand.

3. Approval: After the review, you’ll receive feedback. If your plans meet all requirements, you’ll get approval. If not, you’ll need to make the necessary revisions and resubmit.

Required Documents

Plot Plan: This is a detailed layout of your property. It should show the locations of existing structures, proposed ADU, property lines, setbacks, utility connections, and other relevant features.

Construction Drawings: These include architectural plans, structural calculations, and any other technical drawings. They should be detailed and comply with local building codes.

Zoning Compliance: Ensure your ADU meets zoning requirements. This includes verifying that your property is in a zone that allows ADUs, and that your plans comply with size and setback regulations.

Timeline and Tips for a Smooth Process

Expected Duration: The entire permitting process can take anywhere from 5 to 7 months, not including construction time. Delays are common, so plan accordingly.

Common Pitfalls: Incomplete applications are a major cause of delays. Make sure all required documents are included and accurately completed. Also, be aware of specific local regulations that might affect your project.

Expert Advice:
Stay Organized: Keep all your documents and correspondence in one place. This will make it easier to track the progress of your application.
Be Patient: Given the current backlog, be prepared for delays. Communicate regularly with the planning department to stay informed about the status of your application.
Consult Professionals: Consider hiring experts like architects or permit expediters who are familiar with San Diego County regulations. They can help you navigate the process more efficiently.

By following these steps and tips, you can streamline the process of obtaining a building permit for your ADU in San Diego County. Next, we’ll address some frequently asked questions to further clarify the process.

Frequently Asked Questions about San Diego County ADU Plans

How much does it cost to build an ADU in San Diego County?

Costs can vary, but a general rule of thumb is a few hundred dollars per square foot. According to industry estimates, the cost per square foot ranges between $300-$500. The overall cost includes several components:

  • Site Work: Preparation, grading, and utility connections.
  • Design and Engineering: Architectural plans, structural calculations, and compliance reports.
  • Vertical Construction: Building materials, labor, and finishes.
  • Permitting Fees: Although many fees are waived, some costs still apply.
  • Solar Panel Installation: Required by state law.
  • Site-Specific Requirements: Unique conditions, such as soil reports or septic systems.

Practical Tip: Reach out to professionals for an accurate cost estimate based on your specific project needs.

What are the rules for ADUs in San Diego County?

San Diego County has specific regulations for ADUs to ensure safety and compliance:

  • Size Limits: A detached ADU can be up to 1,200 sq. ft. An attached ADU can be up to 50% of the main dwelling’s size, with a maximum of 1,200 sq. ft.
  • Zoning Requirements: ADUs are permitted in various residential zones. Check your property’s zoning here.
  • Building Codes: ADUs must comply with health and safety codes, including fire safety and structural integrity.
  • Permit Process: You’ll need a building permit, which involves submitting a plot plan, construction drawings, and proof of zoning compliance.

Practical Tip: Consult the County’s ADU regulations and consider hiring experts to help navigate the permit process.

What is the free ADU grant in San Diego County?

San Diego County offers grants to encourage ADU construction:

  • Eligibility: Typically aimed at low to moderate-income homeowners or those willing to rent the ADU to low-income tenants.
  • Application Process: Submit an application detailing your project and financial need. The process involves income verification and a commitment to rent the ADU at reduced rates for a specified period.
  • Benefits: Grants can cover part of the construction costs, reducing the financial burden on homeowners.

Practical Tip: Check the San Diego Housing Commission for the most current grant programs and eligibility criteria.

By understanding these frequently asked questions, you can better navigate the process of building an ADU in San Diego County. If you have more questions or need personalized assistance, consider reaching out to our experts at OneStop ADU.


OneStop ADU Services

Navigating the complexities of San Diego County ADU plans can be challenging, but with the right guidance, it becomes much more manageable. Our goal at OneStop ADU is to simplify the process, making it as smooth and cost-effective as possible for you.

Why Choose OneStop ADU?

We offer a comprehensive suite of services that cover every aspect of your ADU project. From initial design to obtaining permits, our integrated approach ensures that your project progresses without unnecessary delays.

Comprehensive Services

Our team of experts specializes in modern and minimalist architectural designs, but we also accommodate other styles such as contemporary, craftsman, and traditional designs. This versatile expertise allows us to tailor the ADU to your specific needs and preferences.

Design to Permit Processing

We manage the entire design and permitting process, which includes:

  • Initial Consultation: We start with a detailed discussion to understand your vision and requirements.
  • Feasibility Assessment: Our team evaluates your property to ensure it meets all zoning and building code requirements.
  • Design Phase: We create a design that maximizes space, natural light, and energy efficiency.
  • Permit Processing: We handle all the paperwork and interactions with local authorities, ensuring a seamless approval process.

Time and Cost Efficiency

We understand that time is money. Our streamlined process minimizes delays and reduces costs, making your ADU project more affordable. By using pre-approved plans or modifying existing ones, we can save you both time and money.

Final Tips

  • Plan Ahead: Start early to account for any unexpected delays in the permitting process.
  • Choose Wisely: Opt for pre-approved or semi-custom plans to save on design costs and expedite approval.
  • Stay Informed: Keep up-to-date with local regulations and available grants to maximize your benefits.

Building an ADU is a significant investment, but with OneStop ADU, you can rest assured that your project is in capable hands. Our expertise and comprehensive services make us the ideal partner for your ADU journey.

Ready to get started? Contact us today for a free property analysis and estimate. Let’s make your ADU dream a reality!


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