4 Design
ONCE YOU HAVE A SENSE OF WHAT YOU WANT TO BUILD, know what you can build, and have estimated your budget, you can start designing your ADU, which begins with design inspiration and ends with permit-ready plans.
Timeline
The Design phase typically takes 1-6 months. Most ADU projects take 12-18 months to complete, but some extend to 24 months or more.
Key Resources
ADU Guidebook
Every detail you need from start to finish.
ADU Guidebook
Every detail you need from start to finish.
ADU Exercises
Record the details as you go through the process
ADU Exercises
Record the details as you go through the process.
Pre-Approved ADU Plans
See if your location has pre-approved plans.
ADU Process At-A-Glance
A quick overview of an ADU project.
Floorplan examples
Get inspiration from real ADU layouts.
Floorplan Examples
Get inspiration from real ADU layouts.
FAQs
Here are a few of the most frequently asked questions about ADU design. See the content below and our ADU Guidebook for more guidance, resources, and tips for all steps of the process.
Most homeowners choose to work with some type of design professional to plan their ADU and help throughout the process. Bringing on a professional early in the process is often key to getting your ADU approved quickly, managed efficiently, and built cost-effectively. Relevant experience and fit will be critical.
There are a variety of types of designer, and they may be an architect, builder, “designer,” design/build, or a modular/prefab company. If you’re hiring a local individual or team, they’ll likely start the process by visiting your home and talking to you about your ideas and goals. If it seems like a good match, they will prepare a proposal detailing their services and fee. Professionals typically charge for an initial consultation or proposal.
Note that if you’re not using a licensed architect to design your ADU, your plans may need to be stamped by a licensed engineer. Check with your City early on.
See our Exercises for a list of questions to ask a potential architect or designer, our Glossary to be clear on terms, and our Guidebook for more details.
Once you have a design established with your architect/designer, it’s a great idea to discuss it with City staff so they can point out any issues before you prepare your application.
Depending on the city, you may be able to schedule an appointment to speak with a planner or walk in to the Planning Counter or Permit Center. For contact information, see the Local ADU Rules and Contacts.
This is also a good time to reach out to utility agencies (water, sewer, gas, etc.) to inquire about their infrastructural requirements and confirm connection and service fees.
Site-built/Traditional: A traditionally constructed ADU is designed and built specifically to your preferences and property and built on site (“stick-built”). This option allows for a lot of customization and smaller changes to be made throughout the construction process.
Prefabricated/panelized/modular: These ADUs are partially or mostly built in a factory, then shipped to your site to be put together. Sometimes the company will include all services in their fee (“turn-key”), including help with permitting and all on-site construction tasks (e.g., laying the foundation, utility hookups, etc.). Other times you’ll need to hire additional professionals to help.
Designing your ADU
STEP-BY-STEP
BEFORE YOU BEGIN:
It is helpful to have a clear sense of what you want early in the process. An architect or designer can help you brainstorm, but they cannot start designing until you’ve made basic decisions like the type of ADU you want (see Getting Started) and how many bedrooms it will have. Our Exercises can help you think about these questions.
Consider a Pre-Approved or Pre-Designed Plan
Pre-Designed Plans
Plans that have already been designed by an architect or other professional provide a starting point for you to customize, saving you significant time and money. Your local community may have a list of pre-designed plans they suggest, or you can find a designer than sells starting plans.
Pre-Approved Plans
Some pre-designed plans may have already gone through a review process by your local Building Department, saving you even more time and money and making you eligible for faster permit reviews. As of January 1, 2025, every city and county in California is required to accept ADU plans for pre-approval and list them online for homeowners to use.
Visit our Pre-Approved ADU Plans page to find out if your community has an online Plans Gallery or other way of looking at locally pre-approved plans.
Important:
- Not all pre-designed plans or even locally pre-approved plans work on all properties. Ask a processional about the rules for your property before purchasing or committing to using a design.
- All plans require additional planning and permit applications for your property. You most likely need to hire a professional to complete this work.
Helpful Tools
Hire Experienced Professionals
Although you can build an ADU as an owner builder, we strongly recommend hiring a licensed architect or designer and a licensed contractor, or a design/build team, and most homeowners do. Bringing on a professional early in the process is often key to getting your ADU approved quickly, managed efficiently, and built cost-effectively. Relevant experience and fit are critical, and it’s important to look at their past work and check references.
Your team may include one or more of the following:
- Licensed architect or designer to design your ADU and potentially see you through permitting and construction
- Licensed contractor to build your ADU
- Design/build company that designs and builds your ADU
- Modular/prefab company who sells preset designs for modular/prefab homes
Our ADU Exercises include a list of questions to consider when hiring a team, and our Guidebook provides an overview on design contracts and costs.
Helpful Tools
Create Initial Design
Once you have your team in place, you will work with them to design your ADU. Together you will consider size, use, layout, specific project needs (storage, laundry room, etc.), architectural style, and privacy. If you decide to go with a Pre-Reviewed Plan, you will work to customize the plan to your property.
Once you have an initial design, it’s a good idea to discuss it with City staff so they can point out any issues before submitting your permit application. Your design team can attend this meeting to clarify drawings and help you understand requirements.
If you haven’t already, this is also a good time to reach out to utility service providers (water, sewer, gas, etc.) to confirm your design meets their requirements. See the Local ADU Rules and Contact or the Directory in our Guidebook for all relevant contact information.
Helpful Tools
Finalize Plan
Based on your meeting with staff, your team will work through any required changes and prepare the permit application (see Permitting).
