Frequently Asked Questions

Welcome to the Napa Sonoma ADU Standard Plans Program

The Napa Sonoma ADU Standard Plans Program is a multi-jurisdictional effort administered by the nonprofit Napa Sonoma ADU Center in collaboration with local cities and unincorporated counties across Napa and Sonoma.

What is the goal of the program? Our goal is to make the process of building an ADU easier, faster, and more affordable for homeowners so that we can build more housing for our community. This program is a pilot that we hope will scale beyond our region in order to bring more ADU design options to more homeowners.


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The Basics

Napa Sonoma ADU is a nonprofit that works with homeowners and local governments in Napa and Sonoma counties to support ADU development.

  • Resource-rich website
  • Regular webinars
  • Feasibility consultations for homeowners
  • Support via ADU Office Hours

Much of our work has been funded by Napa Valley Community Foundation (also our fiscal sponsor) with support from Community Foundation Sonoma County as well as state grant funds received through several of our jurisdiction partners.

This new program makes it easier to find ADU designs and go through the development review process, saving time and money and connecting ADU designers, architects, and prefab companies with potential customers. It also helps jurisdictions respond to community housing needs.

The program includes an online gallery featuring:

  • ADU plans that have been “pre-reviewed” for compliance with applicable building codes, and
  • Other “off the shelf” ADU designs available to homeowners at reduced cost (these plans still require code compliance review).

All 16 jurisdictions in Napa and Sonoma have helped shape this program and are a part of this work. However, that does not mean that every plan can be used on every site and in every jurisdiction. Do your homework to know what is possible on your property! Also, decisions about which plans will be accepted as “pre-reviewed” is up to each jurisdiction.

When using the program gallery, you will see whether each plan is “pre-reviewed” for your jurisdiction, with a link to more information about your jurisdiction’s complete ADU plan submittal requirements.

Absolutely! We are here to provide you with clear information and education about ADUs, the ADU process, and what makes the most sense for you given your goals and budget. Start at the very beginning on the ADU Center website, and we’ll guide you through the steps you should take BEFORE you select an ADU plan and license it from a designer.

Yes, you can always reach out directly via this webpage to the designer, architect, or prefab company you are interested in purchasing a plan from. However, the Napa Sonoma ADU Center cannot provide you with assistance if you wish to build an ADU outside of our two-county service area and the plan will not be considered “pre-reviewed” outside of these jurisdictions.

The Pre-Work includes everything you need to do to set yourself up for success, assessing items including:

  • Whether your property is eligible to build an ADU (most will be);
  • Your goals for building an ADU;
    The best type of ADU for you;
  • Whether you can reasonably finance your desired ADU.

The Napa Sonoma ADU Center can provide an in-depth ADU Feasibility Consult to get you started on the right path. Our webpage also has tools and resources to help you think through many of these questions.

Be sure you do this Pre-Work before you invest time and money in your ADU project.

The Plans

“Pre-reviewed plans” include both site-built and prefabricated plans that have been reviewed for compliance with applicable building code requirements (though in some cases, local code variations may require further review). Contact your local jurisdiction regarding their pre-reviewed plans process.

NOTE: In all circumstances, a pre-reviewed plan will still need to be tailored for your site and project by the designer or prefab company whose plan you select before submitting it to your jurisdiction for ADU permit approval.

Yes! There are multiple types of prefabricated (“prefab”) ADU options available. All prefab plan options are under the category of “pre-reviewed” because they have been built in compliance with either federal or state building codes. This means that your local jurisdiction does not need to review prefab plan sets for compliance with building codes, but there are site-specific elements of your ADU project that will still need to be reviewed, such as foundation and utility connection plans. Speak with the prefab company whose plan you select to understand the level of support they will provide you through the full ADU permitting and building process.

To learn more about different types of prefab ADUs, watch our on-demand webinar.

Not at this time. Converting a garage or other existing space to living space is a great way to create an ADU, but it is challenging to create standard plans for conversions, which are by necessity very site and structure-specific for each individual project.

Site-built plans are for ADUs constructed on your property. In this gallery you will find site-built plans that have been “pre-reviewed” for compliance with applicable building codes as well as site-built plans that will need to be reviewed through a standard process. Your jurisdiction will determine the level of additional code review required, including the fees for the review. Even if using a pre-reviewed plan, you will need to work with your designer/architect to submit the plan along with additional details about your site (such as a site plan, utility connection plan, etc.) to get a building permit. Speak with the designer or architect whose plan you select to understand the level of support they will provide you through the full ADU permitting process.

Prefabricated plans are ADUs that are largely built off-site in a factory and then transported and installed on your property on a permanent foundation. All prefabricated ADUs are pre-reviewed for building code compliance at the state or federal level. Just like site-built plans, additional site-specific information (such as a site plan, utility connection plan, a foundation plan, etc.) will need to be submitted to your building department to get full permit approval. Speak with the prefab company whose plan you select to understand the level of support they will provide you through the full ADU permitting and building process. Watch our on-demand webinar on prefab ADUs for more information about the different types of prefab ADUs and what to consider when making the decision to go with a prefab ADU.

There were many plans that we thought were great, but which did not make it into the initial short-list of plans for pre-review. We refer to these plans in the gallery as “off the shelf,” since they’re shortcutting what would otherwise be a fully custom design process. Even though they still need to go through the full code review process to get a building permit, they should save considerable time and money. By including these plans in our gallery, we hope to make it easier to find a design that works for you and connect with the designer or architect who can help you get there.

We hope so, yes!

State law requires that jurisdictions issue decisions on complete ADU permit applications within 60 days, and many of our jurisdiction partners have internal policies to do it in an even shorter time period — but in reality, some jurisdictions have struggled to complete ADU permit processing within 60 days because of issues like staff shortages, not receiving complete applications, and more.We are working with jurisdictions to streamline the process for “pre-reviewed” plans, but sometimes there will be site-specific issues that popup or delays on behalf of other involved agencies (e.g., utilities and fire departments). Go to your jurisdiction’s ADU webpage (see list below) to learn more about how they are supporting implementation of ADUs, including their policies and practices around pre-reviewed ADU plans.

Staff from jurisdictions across Napa and Sonoma counties helped our nonprofit review the 55+ plans that were submitted in response to our first-ever statewide Call for Submittals. They helped score each plan based on criteria that included cost, privacy, context/compatibility, adaptability, accessibility and sustainability. We reviewed plans based on these scores, making sure we provided choices across all size categories and that the selections reflected both local and broader statewide architects and designers. Key themes that came up during deliberations included livability (did the unit include storage? space for a washer/dryer? privacy?); accessibility/adaptability (was the unit wheelchair accessible, or could it easily be made to be?); and price point.  In the future, we will re-open the Call for Submittals so that the gallery of plans can grow.

If you are a designer, architect or prefab company interested in more details or submitting your plans, see the Designer FAQs. If you would like to receive an invitation to submit in the future please complete this form.


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Please submit your email and accept our terms and conditions to access designer contact information.

Terms & Conditions

I understand that by contacting the ADU designer or firm and potentially proceeding with the purchase (licensing) of an ADU plan, that I have read, understood and agree to the following terms and conditions:

1 – Approval Authority. I understand that my local jurisdiction’s building department has final review and approval authority for any ADU construction drawings and related permit application materials.

2 – Confirming Site Suitability Prior to Plan Purchase. I understand that it is my responsibility to understand what may or may not be allowed on my property by consulting with my local jurisdiction about requirements, regulations and limitations prior to purchasing an ADU plan.

3 – Plan Ownership and Responsibility. I understand that any plans I purchase are the property of the ADU designer or firm that developed them, and use of those plans are subject to any conditions, requirements or limitations established by the designer or firm.

4 – Liability from Plan Purchase and Use. I understand that any liability or legal action arising from my engagement with a designer or ADU firm or from the purchase and use of their plan shall be governed by the contract I sign with that designer or firm, and that Napa Sonoma ADU, under fiscal sponsorship of the Napa Valley Community Foundation, and Baird+Driskell Community Planning, who developed and manage the ADU gallery, are in no way a party to that contract or in any way, shape or form liable for my use of the plan and resulting ADU.

5 – “Pre-Review” Status. I understand that Napa Sonoma ADU, under fiscal sponsorship of Napa Valley Community Foundation, and Baird+Driskell Community Planning, acting as their contractor, engaged a third-party reviewer, BPR Consulting Group, to review some of the plans featured on the gallery for compliance with state building codes. The letter BPR Consulting Group’s review and conclusions is provided on the site as a courtesy, and represents BPR Consulting Group’s professional judgment based on the information provided to them by the relevant designer or ADU firm. Napa Sonoma ADU, Napa Valley Community Foundation and Baird+Driskell Community Planning do not warrant for the accuracy of the review and are in no way responsible or liable for their work. Further, Napa Sonoma ADU, Napa Valley Community Foundation and Baird+Driskell Community Planning do not claim or represent that BPR’s review letter has any authority in the review and approval process with any specific jurisdiction.

6 – Hold Harmless. I understand that Napa Sonoma ADU, under fiscal sponsorship of Napa Valley Community Foundation, and Baird+Driskell Community Planning have created this gallery as a service to help property owners search for ADU plans that may meet their needs and connect them with the ADU designer or firm that developed and owns those plans. Napa Sonoma ADU, Napa Valley Community Foundation and Baird+Driskell Community Planning in no way warrant or are liable for the quality, constructability or safety of any plan featured on the site or for any financial or legal issues resulting from a property owner’s engagement with a designer or firm located through use of the gallery page.


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Send an email to yourself (or someone else) with a link to this listing and designer contact information. You can also add notes about the listing.