Building an ADU: A Step-by-Step Guide

Are you looking to build an accessory dwelling unit (ADU) but don’t know where to start? Building an ADU can be a great way to add value to your property, create additional living space for family members, or generate rental income. In this step-by-step guide, we will walk you through the entire process of building an ADU from concept to completion. We will cover everything from researching feasibility and planning with an architect to navigating the Department of Building and Safety and hiring the right contractor. You’ll also get an in-depth look at the building process and timeline, including foundation construction, framing, MEP systems installation, drywall and insulation, and fixture and finishes installation. By the end of this guide, you’ll have all the information you need to confidently tackle your ADU project.

We’ve worked on hundreds of accessory dwelling units throughout Los Angeles, Orange County, Ventura County and greater Southern California. GreatBuildz helps homeowners every day to turn their ADU dreams into a reality.

What is an ADU and Why Should You Build One?

An ADU is an Accessory Dwelling Unit, sometimes referred to as a ‘granny flat.’ There are many benefits of constructing an ADU on your property. You can increase your property’s living space, making room for family or rental. The rising popularity of ADUs among homeowners is helping to address the affordable housing crisis. Ultimately, building an ADU can generate rental income, offer additional living quarters, and boost property value.

Backyard ADU

FAQs About Building an ADU

  • What are the benefits?

An accessory dwelling unit relieves many problems and allows for a ton of flexibility. People are building them to use as extra space (an office or guest house), a music or yoga studio, a mancave or she-shed, or a home for their retired parents or grown children.

  • What are the financing options?

There are a number of options worth considering based on your specific situation, and fortunately, more and more lenders are starting to offer ADU loan programs. Explore some options HERE.

  • What does building an ADU cost?

An accessory dwelling unit will vary greatly in cost based on the options and size you choose. The cost for an ADU garage conversion can usually range from $120,000-$180,000 depending on the homeowner’s requirements. Costs to construct a new accessory dwelling unit will generally range from $200,000-$400,000. A safe rule of thumb is to assume any new construction costs $400-$600 per square foot – the bigger the space, the lower cost per square foot.

  • How long does it take to build an ADU?

For a garage conversion, you can expect the entire process to take 6-12 months, depending on where you live. A new accessory dwelling unit will take longer for city plan check and require a longer construction process, so you can expect the entire process to take 12-15 months, with the construction phase lasting 6-9 months.

  • Do I need to hire a contractor?

When looking to build an accessory dwelling unit or even starting to explore the idea, it’s best to search for local, licensed General Contractors. No other contractors are qualified or equipped to do this sort of construction, and using an unlicensed contractor or handyman would be a mistake. Overseeing the project yourself is also very risky.

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Building an ADU Step-by-Step: From Concept to Completion

Building an ADU can be a complicated process – it’s basically a small house, after all! Taking each step one at a time will ensure that you navigate the ADU building process effectively. Following a comprehensive guide will provide you with the roadmap needed to turn your ADU concept into a completed dwelling. From researching feasibility and planning with an architect to submitting plans for approval and meeting Title 24 requirements, each step of the process is essential. With the right contractor and a clear understanding of the timeline, you can confidently move forward with building your ADU.

Los Angeles ADU

Researching Feasibility: Assessing Your Property for an ADU

To determine the feasibility of building an ADU, you need to assess your property thoroughly. Start by considering factors like zoning regulations and property size. Ensure that your property complies with the necessary requirements for constructing a detached ADU or an attached ADU. You may need to obtain a soils report to determine how to make the unit structurally sound. It’s also essential to evaluate the financial feasibility of your ADU project and explore financing options available to you. Familiarize yourself with different types of ADUs (garage conversions, stick-build, pre-fab) and their specific requirements, such as site prep and utility hookups. By researching the feasibility of building an ADU, you can make an informed decision about this independent living space.

Planning and Designing Your ADU with an Architect

Collaborating with an architect is a crucial step in planning and designing your ADU. By working closely with them, you can create a design that meets your needs and preferences. It’s important to discuss the layout and features you want in your ADU to ensure it aligns with your vision. Additionally, your architect will help ensure that your ADU plans comply with local building codes and regulations. Consider incorporating sustainable and energy-efficient elements into your design to maximize efficiency. Getting expert advice will also help you optimize the livable space in your ADU.

ADU Architect

Submitting Plans for Approval: Navigating the Department of Building and Safety

Navigating the Department of Building and Safety is an essential step when submitting plans for approval. The department reviews plans to ensure compliance with zoning and building codes, so it’s crucial to submit accurate and complete plans. Working with an architect can help ensure your plans meet all the necessary requirements. Keep in mind that the plan approval and permitting process may involve multiple rounds of review, so allowing ample time for this step is important. Once your plans are approved, you can move forward with obtaining permits and begin the construction phase.

Meeting Title 24 Requirements for ADUs: What You Need to Know

To ensure your ADU meets the necessary energy efficiency standards, it’s important to understand the requirements outlined in Title 24. This regulation covers various aspects, including lighting, insulation, and HVAC systems. By incorporating specific measures, such as energy-efficient lighting fixtures and properly insulated walls, floors, and ceilings, you can increase the overall energy efficiency of your ADU.

Additionally, exploring options for solar panel installation can further enhance sustainability. To ensure compliance with Title 24, it’s recommended to consult with professionals who are well-versed in these requirements. Their expertise will ensure that your ADU meets all the necessary criteria for energy efficiency.

Getting Contractor Quotes: How to Compare and Choose the Right One

To ensure a successful ADU construction, it’s essential to obtain quotes from multiple contractors. When comparing contractors, consider factors such as prices, timelines, and services offered. It’s also important to review the contractor’s experience and expertise in building ADUs. Take the time to assess their past projects and client testimonials.

Checking references and reviews from previous clients can provide valuable insights. Additionally, inquire about the contractor’s insurance, licensing, and warranties before committing to a contract. By carefully evaluating these factors, you can make an informed decision and choose the right contractor for your ADU project.

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ADU General Contractor

Hiring a Contractor and Establishing a Timeline for Construction

Once you have chosen a contractor for your ADU build, it is important to finalize the contract and establish a clear timeline for each stage of construction. Discuss expectations, milestones, and project management with the contractor to ensure that both parties are on the same page. It is also essential to communicate regularly with the contractor to track progress, address any issues, and ensure that the project stays on track.

Asking for a detailed timeline and schedule will help you stay organized and anticipate the different phases of the construction process. By establishing a strong relationship of trust and communication and setting clear expectations, you can ensure a smooth and timely completion of your ADU construction project.

Download the ADU Construction Checklist

What is the Building Process?

Throughout the building process of your ADU, your contractor will coordinate with subcontractors, inspectors, and suppliers to ensure everything runs smoothly. The first step is site preparation, which involves clearing and leveling the building site and setting the foundation. Once that’s done, the framing and construction phase begins, where the walls, roof, and floors of your ADU are built. Following that, plumbing, electrical, and HVAC installation takes place to ensure all necessary systems and utilities are in place. This seamless process ensures that your ADU is built efficiently and to the highest standards.

Selecting and Ordering Materials for Your ADU Build

When building an ADU, it’s crucial to select the right materials that align with both the design aesthetic and functionality of your space. Consider factors like durability, maintenance requirements, and cost when making your choices. Collaboration with your contractor is key to ensuring material compatibility with the overall design and structure.

Researching suppliers and ordering materials in advance will help you avoid unnecessary delays during the construction process. Additionally, comparing prices and exploring cost-effective options will help you stay within budget. By carefully selecting and ordering materials in a timely fashion, you can ensure the successful completion of your ADU build.

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Foundation Construction: Laying the Groundwork for Your ADU

A strong foundation is crucial for any ADU. It provides stability and longevity to your structure, ensuring it stands the test of time, especially in Southern California. The process begins with excavation, where the ground is prepared for pouring the foundation. Proper materials, such as reinforced concrete, are used to ensure the foundation’s strength.

Inspections will play a vital role in ensuring that the construction meets safety standards and regulations. Additionally, proper drainage is essential to prevent water damage to your ADU. By laying a solid foundation, you’re setting the stage for a secure and durable independent living space.

Framing Your ADU: Building the Skeleton of Your New Space

Framing is the next crucial aspect of constructing an ADU, providing the structural support and framework for your new space. The process involves framing walls, floors, and roofs using appropriate materials to ensure structural integrity. Accurate measurements and calculations are essential during this stage to ensure a precise fit. This phase will also require inspections.

MEP Systems Installation: Addressing Electrical, Plumbing, and HVAC Needs

MEP systems, which encompass electrical, plumbing, and HVAC components, are crucial for a well-functioning ADU. The installation process involves carefully wiring the electrical system and strategically placing outlets throughout the space. Plumbing installation includes the setup of fixtures and pipes, ensuring proper water supply and drainage – if your ADU is detached, you will also have to hook up to the main sewer line, which may require trenching through concrete or landscaping.

HVAC systems provide climate control, ensuring comfort for occupants in all seasons. Hiring professionals for the installation of all of these systems is vital to guarantee safety and compliance with regulations. Their expertise ensures that the ADU’s MEP systems are seamlessly integrated, providing a functional and comfortable living environment.

ADU Designer

Drywall and Insulation: Creating a Comfortable Living Environment

Installing drywall and finishing surfaces involves hanging sheets of drywall, taping seams, and applying joint compound for a smooth, seamless finish. In addition to providing a finished look. Drywall also helps with soundproofing and fire resistance.

Insulation is equally important, as it regulates temperature and reduces noise transmission. Proper sealing and moisture control are necessary to prevent any issues related to humidity or water damage. Insulation also contributes to energy efficiency, resulting in potential cost savings for homeowners.

Fixture and Finishes Installation: Putting the Final Touches on Your ADU

Putting the final touches on your ADU involves the installation of fixtures and finishes that not only serve functional purposes but also enhance the overall aesthetics of your space. Plumbing fixtures, lighting, and appliances are carefully installed to ensure proper functionality and alignment. Cabinets and countertops will also be installed in this phase.

It is crucial to use high-quality materials for durability and to create a cohesive look. Taking accurate measurements ensures a seamless fit. Finishes such as paint, flooring, and window treatments add the final touch, creating a welcoming and visually appealing environment. By paying attention to these details, you can transform your ADU into a comfortable and stylish living space.

Detached ADU

Ready to Start Your ADU Project?

Building an ADU is a complex process that requires careful planning and execution. From assessing the feasibility of your property to designing and constructing your ADU, every step plays a crucial role in ensuring a successful project. It’s important to navigate through the various stages, including obtaining approvals, meeting building requirements, and selecting the right contractor.

Remember to take your time, do thorough research, and consult with professionals when needed. Building an ADU can be a rewarding investment that adds value to your property and provides additional living space for you and your loved ones.

GreatBuildz is a free service that connects homeowners in Los Angeles, Ventura, and Orange County with reliable, thoroughly screened general contractors and provides project support from start to finish.


Hi, we're Paul and Jon - Co-Founders of GreatBuildz. We believe everyone deserves to find a great contractor, have a stress-free renovation, and enjoy their beautiful new space. There are so many contractors out there and it's often hard to tell the good from the bad... until it's too late. We started our company to help simplify your contractor search and help you have a stress-free renovation experience. We're always available to help, no matter where you are in the process. Click here to learn more about our story.

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