Accessory Dwelling Units (ADUs) in San Francisco

What Is An ADU?

What do a granny flat, an in-law unit, a guest house, and a cottage have in common? They are all considered to be ADUs, or accessory dwelling units. An ADU can be an independent residential unit located on the same lot as a single-family home, or it can be an additional dwelling that uses underutilized space, such as an attic, storage room, or garage. In San Francisco, a first-floor garage space is the most common ADU conversion.

San Francisco adopted its ADU program in certain districts in 2014, and has since expanded city-wide. A number of state bills revising requirements and processes regarding ADUs went into effect on January 1, 2020. Because there may be additional code requirements and legislative amendments, please refer to San Francisco Planning for current information.


ADUs can add living space to existing structures and lots, which is very important and significant in a dense city such as San Francisco. There’s also a very distinct benefit of adding an ADU in San Francisco, and that is, if you build an ADU while doing the structural work of a seismic retrofitting, you can offset the construction costs.

There are many other reasons why adding an ADU is beneficial for property owners. Here are a few:

  • ADUs provide a supplemental income source for a homeowner
  • ADUs can increase the value of your property
  • ADUs allow you to increase the size of your living space without having to move
  • ADUs provide living space for extended families while maintaining privacy; seniors can age in place with their families
  • ADUs can add working space to your dwelling—more important now than ever as working from home becomes increasingly necessary
  • ADUs are less costly to build than homes in new multifamily buildings


If you own a single-family-home you may be eligible to add an additional residential unit to your existing home. If you own a multi-family building you may be eligible to add additional residential units, depending on how many units you have and what zoning allows. As of 2019, if the zoning district permits residential uses and includes existing residential buildings, then the lot is eligible for ADUs. offers a way to check your eligibility online.




exterior adu building photo


The local ADU program allows adding ADUs to existing or proposed single- and multi-family buildings while the state ADU program allows the addition of ADUs, detached ADUs, or Junior ADUs to existing or proposed single-family buildings. Here are some key requirements and guidelines around building an ADU in San Francisco; visit SF Planning for more information:

An ADU can’t take space from the existing residential unit

The ADU must be constructed within existing envelope of the dwelling

In multi-unit buildings, ADUs can be constructed in conjunction with new construction of a multi-unit building, or within the existing built envelope

For existing or new single-family properties, one converted ADU is allowed per property

If four or less legal dwelling units are on a lot, one ADU is permitted

For existing multi-family properties, one converted ADU is allowed per property; two detached ADUs are allowed per property (City Codes may require separation between buildings)

Parking spaces may be removed to accommodate an ADU

You can increase the height of your building to add an ADU if you are simultaneously undergoing full seismic retrofitting of the entire building

New ADUs in multi-unit buildings will likely be subject to rent control

ADUs are ineligible for the Short Term Rental program

In most cases an ADU cannot be sold separately from the main property

For up-to-the-minute information around ADU codes and requirements in San Francisco, visit the SF Planning website or email Refer to the SF Planning ADU Handbook for more information around ADU codes, design standards, and prototypes.


According to the City of San Francisco, if you are planning to “build, demolish, renovate or expand a home, or add one or more dwelling units to an existing residential building”, you will need a building permit. Prior to doing detailed design of your ADU project, you can schedule a Pre-Application meeting with the Department of Building Inspection (DBI). This meeting brings together key staff from Planning, Building and Fire to review ADU projects. offers a step-by-step guide around the process to adding an ADU unit to your property. These steps include:

1. See if you can add new units to your residential property—check the rules online to find out what you can build

2. Contact the City about your ADU—discuss your project first with a City planner

3. Design your ADU—draft architectural plans and submit your plans with your permit application; homeowners usually hire an architect or designer to create these plans


Costs vary depending on type of unit and existing structure. You can find information about construction and permit costs in the SF Planning ADU Handbook . The most common way to finance an ADU is via a home equity loan, which makes sense because you are making improvements to your property and adding value. A home equity line of credit, or HELOC, is much like a credit card; the borrower is not advanced the entire sum up front. A HELOC uses a borrower’s equity in their house as collateral.


Property taxes will increase only the marginal value of the ADU. California assessors treat ADUs like a home addition, so the construction of an ADU will trigger a reassessment, which will actually be a blended assessment. (Keep in mind that renting out your ADU will likely increase your income tax.)

If you have any additional questions that I can answer around adding an ADU to your property, please let me know! Rules and regulations can be confusing and can change rapidly, and I’m here to offer you advice and to send you in the right direction! Call us at 415-735-5867 or email us at

November 2, 2020
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