What is an ADU?
Accessory dwelling units (ADUs) come in many shapes and sizes but are always a self-contained home that is legally part of the same property as the primary residence.
They must have a kitchen, bathroom, and place to sleep, and can range from small efficiency studios to 1,200-square-foot homes with multiple bedrooms. ADUs are also often called granny flats, backyard cottages, in-law units, or converted garage or basement apartments.
Types of ADUs
ADUs and JADUs (Junior ADUs) can take many forms, each with their own benefits and challenges. Under California state law, homeowners can now build both an ADU and a JADU on their property.
Timeline
Building an ADU is an investment of time as well as money. Most projects take one to two years to complete, with interior conversions being the fastest.
Where to start?
The best place to start is with an ADU Feasibility Consult. You’ll meet with an ADU expert and receive a customized ADU Feasibility Report about your property and your local ADU rules.
FAQs
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Accessory Dwelling Units (ADUs) come in many shapes and sizes but are always a self-contained home that is secondary to the main house and legally part of the same property. They must have a kitchen, bathroom, and place to sleep, and typically range from efficiency-size studios to either 1,000 square feet or 1,200 square feet homes with multiple bedrooms. The maximum size depends on the jurisdiction. Until January 1, 2025, there is no requirement to live in the main house or the ADU.
Junior Accessory Dwelling Units (JADUS) are smaller units of up to 500 square feet of space within the existing space of a single-family home (including within an attached garage). JADUs may be limited to an efficiency kitchen (sink, cooking appliance, fridge, and small counter) in some jurisdictions. Some JADUs have their own bathroom and some share with the main house. Construction costs for JADUs are typically much lower. For JADUs, the property owner must live in the primary unit or the JADU.
State law now allows homeowners to have both a JADU and a regular ADU on their property.
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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.
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This site walks you through each part of the ADU process, from gathering initial inspiration and learning what you can build through construction and becoming a landlord or moving in.
The best place to start is with a customized ADU Feasibility Consult to understand your specific property and local ADU rules.
You can also use our Process Map resource for an overview of the process and some initial issues to consider as you get started.
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Unfortunately, our nonprofit is unable to provide support with ADU projects outside of Napa and Sonoma Counties. We recommend that you check out the Casita Coalition and reach out to your local planning department for assistance with next steps on your ADU project. Thank you for reaching out, and we wish you the best of luck with your ADU build!
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We're so glad that you're interested in being added to our nonprofit's vendor registry!
We are currently accepting submissions from builders/general contractors, architects/designers, prefab companies, and engineers via our page here. Please review the comprehensive instructions on the webpage, and if you have any questions don't hesitate to let us know. If you are another vendor type, please feel free to share your company name, website, and contact information with us as well as your vendor type and we will add you to our list to circle back to when we are accepting your vendor type for the registry.
If you are a designer, architect or prefab company interested in being added to our Napa Sonoma ADU Standard Plans Program please sign up for our wait list here.
“When you need an ADU, it’s already too late.
It’s better to plan ahead of time and rent it out until a family member needs it.”
– SONOMA RESIDENT
Benefits for Owners and the Community
Building and renting an ADU is truly a community service — ADUs often provide homes for the local workforce and small families who have difficulty finding local housing that meets their needs.
For homeowners, there are many reasons to build an ADU — rental income, safe and convenient housing for relatives, flexibility over time, and many others.
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