Phase Four
Design
- Identify what you want in a design
- Understand the design process and professionals involved
- Hire a professional team to create your design
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.
What is the difference between a site-built and a prefabricated or manufactured ADU?
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 (“turnkey”), 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.
What is the difference between an ADU and a JADU?
Accessory Dwelling Units (ADUs) come in many shapes and sizes but are always a self-contained home that is usually smaller than the main house and legally part of the same property. They must have a kitchen, bathroom, and place to sleep, and typically range from studios under 500 square feet to large homes with multiple bedrooms.
Junior Accessory Dwelling Units (JADUs) are within the footprint of your home (or attached garage) and less than 500 square feet. They can share a bathroom with the main home and/or have an efficiency kitchen (sink, cooking appliance, fridge, and small counter). Construction costs for JADUs are typically much lower. In most cases, the property owner must live on site in either the main home or the JADU.
State law now allows homeowners to have both a JADU and a regular ADU on their property.
No room behind or next to your main home? You can build it in your front yard instead.
When do I show my designs to local Planning or Building staff?
Once you have a design established with your architect/designer, it’s a great idea to discuss it with City or County staff by visiting their permit counter, so they can point out any issues before you prepare your application. See our Worksheets for questions you might want to ask.
How do I find an architect or designer?
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.
The American Institute of Architects provides helpful information for homeowners and maintains a local East Bay chapter website where you can find professionals accepting new work.
See our Worksheets for a list of questions to ask a potential architect or designer.
How large can my ADU be?
According to state law, you can build an ADU up to 800 square feet, as long as rear and side setbacks are at least 4 feet and it is not above 16 feet tall. Otherwise, size limits depend on your property. No room behind or next to your main home? You can build it in your front yard instead.
See the Learning the Rules guide for more details.
Step by Step
Designing Your ADU
Design
Step 1
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
Design
Step 2
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.
First, you’ll likely get conceptual drawings – drawings based on measurements of your property (perhaps a property survey), local rules, and the type and size of ADU you want. These drawings can also be helpful in finalizing what you want.
Once conceptual drawings have been approved, you’ll get refined drawings that include structural and design components.
Once you have an initial design, it’s a good idea to discuss it with local Planning or Building staff so they can point out any issues before submitting your permit application. Your design team can join you 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 Contact page for all relevant contact information.
Design
Step 3
Finalize plan
Based on the initial discussion with City or County staff, your team will work through any required changes and prepare the permit application (see Permitting).
Many homeowners also get construction drawings from their designer that provide all the details needed for a contractor to bid on the project (see Construction). Potential contractors will likely want to visit the site along with seeing the drawings.
