Double ADU Duplex

1175 SF
1, 2
Two-story ADU with two floor plan options. The design is unique in that you can build one ADU with the option of adding a second one later. The design works either a standalone ADU or as a duplex.

Basic details


1175 SF

Plan Type



1, 2


To help abate the state-wide housing crisis, the California state government recently passed legislation to ensure local municipalities adopt policies to permit accessory dwelling units (ADUs) on lots zoned for single-family residential use. This effectively makes R-1 zoning (single-family) into duplex (two-unit) zoning. Some municipalities are even now looking at ways to permit two ADUs on a single-family lot as well as increasing height limits to allow two-story ADUs. The Double ADU Duplex concept anticipates these coming changes to single-family residential zoning. The ADU is designed to be flexible and easy to build. Inspired by the aesthetics of a backyard shed, the simple gable form and corrugated metal siding with darkened aluminum details lends the ADU a welcoming yet understated design. An optional 10’-0” deep deck in the front of the ADU provides semi-private outdoor space with enough room for grilling and small dining. The ADU is designed with the latest thinking in energy and water efficiency in mind. For example, fully electric appliances and heating systems mean natural gas is not required, thus preventing methane greenhouse gas emissions. An energy-efficient ductless mini-split heat pump system heats and cools the space while an electric tankless water heater heats the ADU’s hot water supply. Optional solar roof photovoltaics and a home battery storage system can also help reduce reliance on the regional electrical grid. In addition, low-flow plumbing fixtures help minimize water use. The exterior walls and roof assemblies are designed to Passive House standards with a high-performance insulated approach, yielding high R-values and reducing the demand on energy to power the space.

Pre-reviewed jurisdictions

Click each jurisdiction to access their ADU webpage and/or resources.

This plan has not been pre-reviewed by any participating jurisdictions. But that’s okay! You can still use it. It will just need to go through their standard review process.

NOTE: This program is currently in beta launch and we’re working on adding more “pre-reviewed” plans. Check back often for updates!

IMPORTANT: Even “pre-reviewed” plans must be submitted along with additional project-specific information for final review and permit approval by your jurisdiction’s building department.


Click or hover each item for a description. 


Click the images to open a slideshow.

Floorplan variations

There are two floor plans options within the same 17’-6” x 38’-0” building footprint: either a 1 bed/1.5 bath model (1,000 SF) or 2 bed/1.5 bath model (1,175 SF) Option A has a double-height space in the living room with a bonus ‘office’ mezzanine above. Option B adds a second bedroom in the space above the living room. The idea is that one could easily add two of these ADUs side-by-side to effectively create a backyard duplex.

Cost Information

License fee:


The license fee is what the designer will charge you to use their plan.

Contact the designer to move forward with this plan. 

Estimated construction cost

Exact costs vary based on site conditions, supply costs, labor costs, etc.

$350,000 - $450,000 (depending on which floor plan is selected, level of finish & fixture quality, fluctuations in material & labor pricing)

Professional fee

The rate or cost the designer will charge to complete the plan for your specific parcel and project.

$150 per hour

Other estimated expenses

- Structural Engineering - Title 24 Energy Report - Civil Engineering - Landscape Design - Local Permitting Fees

Additional Information

If the designer supplied any additional information about this design, it is included below.

The double-height (two-story) accessory dwelling unit is a relatively new concept that responds to California cities and towns relaxing local height limit restrictions. With a compact footprint, this ADU model allows you to preserve more ground area in your backyard while being able to accommodate more square footage than you otherwise would in single-story ADU.

Build this adu

1. Schedule an ADU feasibility consult to get started

Check what types of ADUs you can build on your property and get support with project planning, determining potential costs, and more from the Napa Sonoma ADU Center.
This link takes you to the Napa Sonoma ADU Center website

2. Contact the designer

To move forward with this plan, contact the designer using the information included at the link below.

Email this listing

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


We're glad you're here.

This is our beta launch. Please check back for:

Thanks for visiting. Enjoy browsing our gallery of plans!


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.


To move forward with this plan, please contact the designer using the information below.

Plan name:

Double ADU Duplex



Email address:

Other contact information:

Phone: (415) 972-9086

Email these details

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.