Frequently Asked Questions for Designers
This page is geared towards designers, architects, and prefab ADU companies.
Welcome to the Napa Sonoma ADU Standards 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.
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 (14 cities and 2 counties) have helped shape this program and are a part of this work. This is one of the first comprehensive, multi-jurisdiction programs of its type in the country. Each jurisdiction decides which plans plans they will accept as “pre-reviewed,” with a third-party reviewer conducting code reviews for the selected site-built plans. Some jurisdictions may opt to also conduct their own parallel review.
When using the program gallery, homeowners are able to see whether a listing is “pre-reviewed” in their jurisdiction. Each jurisdiction listed in the “pre-reviewed” section of an individual plan page links to more information about the complete ADU plan submittal requirements for their jurisdiction.
Click here for a video tour of the ADU gallery to understand how it works.
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.
Pre-Reviewed Plans
“Pre-reviewed plans” include both site-built and prefabricated plans that have been reviewed for compliance with applicable building code requirements. In some cases, local code variations may require further review or preclude you from using a plan for your specific site (e.g., due to a Historic District, flood plain, slope, etc.).
NOTE: In all circumstances, a pre-reviewed plan will still require additional information and tailoring before it can be submitted to a jurisdiction for ADU permit approval.
If your plan is chosen to be “pre-reviewed” then we will request a submittal for additional documentation, such as a full-planset, structural calculations (if applicable), Title 24 analysis with the four standard orientations, etc. The submittal will be reviewed by building department reviewers and/ or a third-party reviewer, and if approved it will be listed as pre-reviewed.
See the Pre-Review Submittal Checklist (opens in a new tab)
We hope that use of a “pre-reviewed” plan will reduce the time it takes for an ADU permit application to be approved, but we cannot guarantee it. We are encouraging participating jurisdictions to provide further reduced review times as well as reduced review fees, but those decisions are entirely up to them and the other agencies involved in their review processes (e.g., utilities and fire districts). We believe that over time, having permit-ready plans that jurisdiction staff have seen before and are familiar with will result in faster reviews, whether as an official policy or due to it being part of their regular practice.
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.
Staff from jurisdictions across Napa and Sonoma counties helped our nonprofit review the 55+ plans that were submitted for consideration by designers, architects, and prefab companies in our first-ever statewide open Call for Submittals. Staff were asked to score each plan based on the criteria set forth in the Call for Submittals, including 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 plan to re-open the Call for Submittals so that the gallery of plans can continue to grow.
If you would like to receive an invitation to submit in the future please complete this form.
Yes. Once we have this first version of the program up and running, we hope to be able to add more plans, including additional permit-ready plans that have been reviewed for code compliance by one or more of our jurisdiction partners.
Be sure to sign up on our interest list to be informed about opportunities.
We plan to make this part of the program in the future, including for modular building plans, recognizing that soils types vary across the two county-area and that slope issues will need to be addressed on a site-specific basis.
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.
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.
Designer FAQs
This program allows you to connect with more homeowners interested in purchasing your ADU plans, at no cost to you. The Napa Sonoma ADU Center and participating jurisdictions conduct significant community outreach and education within our community to spread the word about ADUs to homeowners. By being a part of the program gallery, your brand will be marketed to thousands of homeowners.
In return for being featured in the gallery we ask designers to establish a “license fee” that you will charge for use of your design. We do not mandate what the fee should be, but recommend a maximum fee of $1,000. The idea is to sell your plan multiple times to recoup your design costs. The fee will be stated on the site along with estimated construction costs so that homeowners can shop with confidence. They can then choose to work with you to complete their full ADU permit application (e.g., site plan) or can choose to work with an architect of their choice (in which case we recommend having them sign a liability waiver).
We launched the beta version of the program in May 2022 and plan to begin adding additional designers to the gallery on a rolling basis in the future. Add yourself to our interest list in the meantime. We will reach out to you when we reopen the program for additional submissions.
If you already have a plan in the gallery that is not pre-reviewed and you want it to be, or you want to add a plan and make sure it’s pre-reviewed, we intend to offer a fee-based option for designers to engage our third-party reviewer to conduct the initial code review. Please note, that the decision of whether to consider the third-party reviewer’s code check as being sufficient for pre-review status lies with each of the participating jurisdictions. We expect to learn how best to make this process work for everyone after launching our beta version of the program in May 2022.Be sure to sign up on our interest list to be informed about opportunities.
Please fill out this online form.
Any edits or updates to your plan listing may take several days to update as our staff reviews each listing.
