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.

See more in our webinar about prefab and manufactured ADUs.

Accessory Dwelling Units (ADUs) come in many shapes and sizes but are always a self-contained home that is 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 efficiency-size studios to 1,000-square-foot homes with multiple bedrooms.

Junior Accessory Dwelling Units (JADUS) are smaller units of up to 500 square feet of space within or attached to a single-family home (including within an attached garage). JADUs typically include an efficiency kitchen (sink, cooking appliance, fridge, and small counter). Some JADUs have their own bathroom and some share with the main house. Construction costs for JADUs are typically much lower than a regular ADU. Unlike regular ADUs, 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.

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.
You can also use our Process Map resource for an overview of the process and some initial issues to consider as you get started.

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!

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.

The best place to start is with a customized ADU Feasibility Consult to understand your specific property and local ADU rules. At the same time, you can work on thinking about what you want and looking at other ADUs to get a sense of what’s possible. Once you have some ideas in mind, you can move on to Learning the Rules to figure out what you can build on your property (the feasibility study will help with this too).

You can also use our Process Map resource for an overview of the process and some initial issues to consider as you get started.

Building an ADU is an investment of time as well as money. Most projects take one to two years to complete. Typically, it takes homeowners one to three months to get started and assemble their team, then one to six months to develop plans, meet with the city, and submit the application. Depending on what permits are required, how many rounds of review are required and how quickly a homeowner and their project team can respond to comments, it will take one to three months to get permits. Construction usually takes six to twelve months.