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Accessory Dwelling Units

Building an Accessory Dwelling Unit in Brisbane

Illustration of single-family home with accessory dwelling unit

What is an ADU, and Why Should I Build One?

Accessory dwelling units (ADUs), also known as second units or granny units, are small homes that contain everything someone needs to live (kitchen, bathroom, and sleeping area) on the same property as an existing single-family home. ADUs can be separate, detached buildings on the same property, or can share walls or other structure elements with the main home. They can also be created within existing space in a single-family home.

Not only can ADUs benefit homeowners by providing a potential income source or shared household responsibilities, but they also provide a valuable source of affordable housing throughout the City, which currently has a very low rental vacancy rate for traditional multi-family rental units. ADUs are often rented at below market rates, or are occupied by family members or caregivers at no charge, depending on the situation.

Can I Build an ADU on My Property?

You can build an ADU on any lot in the R-1, R-2, R-3, R-BA, or SCRO-1 zoning districts where there is an existing or proposed single-family home. Only one ADU is allowed per lot/single-family home. If you are not sure if your property is in any of these zoning districts, call the Community Development Department at (415) 508-2120 or check out the Zoning Map.
ADUs must comply with the ADU regulations in BMC Chapter 17.43. They must also comply with the development standards of your zoning district, like maximum floor area, lot coverage, and building height, and minimum setbacks from property lines. Check out this handout summarizing the development standards of each zoning district that allows ADUs.
Please note: owner occupancy of either the single-family home or ADU is required. This means that you may not rent out both the single-family home and the ADU simultaneously. If your home is located in the R-2 or R-3 zoning district and you are interested in adding an additional dwelling unit to your property but do not plan on residing on the property, contact the Community Development Department (see contact info at the bottom of the page) to discuss the permitting process to establish a duplex or dwelling group on your property. Please note that parking requirements are different for duplex or dwelling group projects.

What Permits are Required to Build an ADU?


A planning permit is only required only for ADUs resulting from new construction; that is, if you are building a new attached or detached dwelling unit requiring a new foundation, walls, and roof. Make sure you have the necessary plan documents listed in the ADU planning permit application checklist (link below) before submitting your application.
ADU projects that do not proposed new construction and only convert existing living space within an existing structure (accessory structure or the primary home) require only a building permit (see below); no planning permit is required.

All ADUs require a building permit. Visit the Building Permit webpage for an overview of the City's building permit fees, procedures, and requirements. The building permit application may be submitted online or in person at the Community Development Department counter at City Hall. Building permit applications are reviewed by all City departments, including Planning, Building, Fire, and Public Works to make sure the plans comply with health and safety codes.
Building permit fees generally will include the following:

ADU Building permit fee table


Other fees may be assessed by the Public Works Department if your project requires an encroachment permit, grading permit, or changes to the property's connections to the City's water and sewer systems. A summary of permits that may be required and current fees for those permits is provided below. Please contact the Public Works Department, Administrative Assistant Diane Cannon, at (415) 508-2120 or dcannon@brisbaneca.org to confirm applicable fees and current fee amounts:
  • Encroachment permit
  • Grading permit
  • Paving permit (new paved areas only)
  • Truck haul permit
School district developer fees are also required for ADUs resulting from new construction based on the square footage of new construction. For more information on school district developer fees, which are updated annually, refer to the Building Permits webpage.

Looking for Inspiration?

Check out San Mateo County Home for All’s Second Unit Center webpage for resources on ADU designs, a calculator for ADU planning and construction costs, and other resources for homeowners.

Get Help with the Approval Process

If you’re interested in building an ADU, you can email, call, or visit the Community Development Department to learn more about the permitting process.
Community Development Department
Brisbane City Hall
50 Park Place
Brisbane, CA 94005
Ph: (415) 508-2120
Counter Hours:
Monday, Tuesday, Thursday: 8 AM – 5 PM
Wednesday: 8 AM- 8 PM
Friday: 8 AM- 1 PM