ADU Construction and Conversion Insights

How Long Does it Take to Build an ADU (Accessory Dwelling Unit)?

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25 min read

Learn about the complete timeline and key steps involved in building an ADU, from initial design to final construction.

Construction phase of an ADU with visible wooden framing, windows, and electrical systems in progress.


While building an accessory dwelling unit (ADU) is an exciting venture that offers additional living space, potential rental income, and increased property value, understanding how to build an ADU can feel daunting. However, understanding the ADU construction process is essential for success. The process can be complex and lengthy. This blog will provide a comprehensive timeline for ADU construction, covering the design and development phase, permitting timeline, building process, and tips for a successful project.

How long does it take to build an ADU?

How long does it take to build an ADU? The timeline for building an accessory dwelling unit largely depends on your ADU and several crucial factors, including design complexity, the permitting process, and the overall construction process and ADU plans. On average, the entire process can take anywhere from 7 to 18 months.

ADU Design & Development

Designing an ADU typically takes about 8 weeks. This phase involves working with an architect or designer to create plans that meet your needs and comply with local regulations. Factors that can influence this timeline include the design’s complexity and any revisions the homeowner requires.

Important Design Considerations for Your ADU Plans

When designing your ADU, consider the following:

  • Size and Layout Determine the size of the ADU based on your property and intended use. Optimize the layout for functionality and comfort.
  • Architectural Style Ensure the design complements the main house and the neighborhood’s aesthetic.
  • Accessibility Consider including features that enhance accessibility, such as wider doorways and ramps.
  • Energy Efficiency Incorporate energy-efficient elements to reduce long-term utility costs and meet local building codes.

How long does it take to design an ADU?

Designing an ADU typically takes about 8 weeks. This phase involves working with an architect or designer to create plans that meet your needs and comply with local regulations. Factors that can influence this timeline include the design’s complexity and any revisions the homeowner requires.

ADU Permitting Process and Timeline

The permitting process for an ADU can vary widely; expect to go through a review process that will impact both time and cost. The process includes submitting your plans to the local building department, waiting for approval, and addressing any required revisions. Factors such as the complexity of your project, local regulations, and the workload of the permitting office can impact this timeline. Here’s a detailed breakdown of what to expect when planning and obtaining a building permit for your new ADU.

Key steps in the ADU permitting process:

  • Submit Your ADU Permit Complete application and plans submission.
  • Permit Review Local authorities review and request revisions before they issue your building permit, as mandated by ADU legislation.
  • Approval Receive approval and necessary permits.
  • Common Challenges Navigate potential delays from incomplete applications or additional requirements through a thorough review process to ensure your ADU meets all necessary standards.

How Long Does it Take to Get an ADU Permit?

The permitting process can take anywhere from 2 to 8 months. California law mandates that an ADU construction permit must be approved or denied within 60 days of submission, making it crucial to have a streamlined design build approach. However, practical delays such as incomplete applications, technical errors, and the workload of local building departments can extend this timeframe. To minimize delays, ensure your application is complete and accurate, as any inaccuracies may take longer to correct and extend your ADU timeline.

Submit Your ADU Construction Plans to the City

Submitting your permit involves several steps:

  • Application Submission Complete and submit the necessary forms to the local planning or building department.
  • Fee Payment Pay the required permit fees, ranging from $2,000 to $10,000, depending on the location and project complexity.
  • Plan Review The submitted plans undergo review by various departments, including planning, building, and fire.

Common ADU Permit Challenges and How to Overcome Them

  • Incomplete Applications Ensure all required documents are complete and accurate to avoid delays.
  • Technical Errors Double-check your construction drawings for any technical errors before submitting your plans to the city to avoid revisions.
  • Workload of Local Departments Be prepared for potential delays due to the high volume of applications in some areas.

Your ADU Building Timeline

The construction phase of an ADU project involves several critical steps that must be carefully coordinated to ensure timely completion, starting with a clear scope of work and thoughtful design choices. Factors such as design complexity, weather conditions, and material availability significantly impact the overall timeline, so working with a skilled ADU builder can streamline the process of building ADUs. Proper planning and collaboration on construction plans with experienced contractors are essential to streamline the process and avoid delays when building your ADU.

Key stages in the ADU building process:

  • Site Preparation Clearing and preparing the land for construction.
  • Foundation and Framing Laying the foundation and building the frame of the ADU.
  • Plumbing and Electrical Installing essential systems for functionality.
  • Interior and Exterior Finishes Completing the interior and exterior design elements.

How Long Does it Take to Construct an ADU?

The construction phase typically takes about 3 to 4 months for site-built ADUs and 6 to 9 months for prefabricated units. However, the timeline can take longer based on the complexity of the project, weather conditions, and material availability, all of which impact how quickly you can build the ADU. Efficient project management and early material procurement can help mitigate potential delays and keep the project on schedule.

What Can Slow Down the ADU Build Process?

Several factors can cause delays in the set of construction activities and influence the time it takes to construct an ADU.

  • Weather Conditions Adverse weather can halt construction activities.
  • Material Shortages Supply chain issues can delay the delivery of essential materials.
  • Homeowner Decisions Changes in design or finishes during construction can lead to significant delays.

7 Common Delays to Avoid in Your ADU Build: Insider Tips from ADU Experts

  • Incomplete Planning Ensure thorough planning before starting construction; your team will work with you to explore every potential ADU configuration.
  • Permit Delays Submit complete and accurate applications to avoid back-and-forth with the planning department.
  • Design Changes Finalize the design early to prevent mid-construction changes.
  • Material Shortages Order materials well in advance to avoid supply chain delays.
  • Weather Delays Schedule construction around local weather patterns.
  • Contractor Availability Book contractors early to ensure their availability.
  • Inspection Delays Schedule inspections in advance to avoid waiting for inspector availability.

Additional Tips for a Successful ADU Project

Effective project management is crucial for a successful ADU build. Regularly communicate with your contractor to stay updated on progress and promptly address any issues. Scheduling regular site visits and progress meetings can help ensure the project stays on track and meets your expectations. Familiarizing yourself with local ADU regulations and new construction codes can also help avoid delays and legal complications.

Here are a few more things to consider:

Budgeting for Your ADU Project

Create a detailed budget that includes all costs, such as design, permits, construction, and unexpected expenses. It’s advisable to set aside a contingency fund for unforeseen costs.

Choosing the Right Materials and Finishes for Your ADU

Select durable, high-quality materials that align with your design vision and budget. Prioritize materials that offer long-term value and require minimal maintenance.

Maximizing Space and Functionality in Your ADU Floor Plan

Design the ADU to maximize space and functionality. Consider multi-purpose furniture, built-in storage, and open floor plans to create a comfortable living environment.

Top 5 Reasons San Diego Real Estate Agents Love ADUs

  • Increased Property Value ADUs significantly boost the property value, making them attractive to potential buyers.
  • Rental Income Potential Homeowners can generate rental income, offsetting mortgage costs.
  • Flexible Living Spaces ADUs provide flexible living arrangements for extended family or guests.
  • Sustainable Living ADUs promote sustainable living by utilizing existing land efficiently.
  • Market Demand The high demand for ADUs in San Diego makes properties with ADUs more desirable.

Conclusion: Making Your ADU Build Journey Smooth and Efficient

Building an ADU can be complex, but you can navigate it successfully with careful planning, the right team, and a clear understanding of the steps involved. By following the tips and timelines provided, you can make your ADU project a rewarding investment.

In summary, constructing an ADU takes time and effort, but the benefits are worth it. Each phase is crucial for a successful outcome, from the initial design and permitting to the final build. Challenges such as weather delays, material shortages, and permit issues can arise, but with proper planning and a reliable team, these obstacles can be overcome.

Whether you’re near Hotel Del Coronado in Coronado, Balboa Park in San Diego, or Vista in Vista, Better Place Design & Build is here to help. As the best ADU builders in San Diego, we’re dedicated to making your next ADU project a success. Get started with us and schedule your free consultation today!


The timeline for building an ADU varies, but it generally takes 7 to 18 months from start to finish, including design, permitting, and construction.

While California law mandates a 60-day approval period for ADU permits, practical delays can extend this process to several months.

Permit costs range from $2,000 to $10,000, with additional city fees ranging from $3,000 to $11,000.

The permitting process in San Diego typically takes 3 to 9 months, depending on project complexity and local department workloads.

The value of an ADU can be calculated using methods like the value per square foot, percentage increase in property value, rental income approach, and sales comparison approach.

Requirements include minimum unit size, height limits, setback requirements, parking provisions, utility connections, fire sprinklers, solar panel installation, rental restrictions, and impact fees.

An ADU can add $200,000 to $500,000 to a property’s value, depending on various factors such as size, type, and location.

Building an ADU can be challenging due to permitting complexities, design constraints, financing issues, and regulatory compliance, but these challenges can be managed with proper planning and professional assistance.

The first step is conducting a feasibility study to determine the project’s viability and ensure compliance with regulations.

Hire a contractor by defining your project scope and budget, researching and identifying potential contractors, verifying credentials, requesting and comparing bids, checking references, conducting interviews, and signing a detailed contract.


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