Design an ADU that meets City codes

After you decide to build an ADU, you must create plans to submit to the City. Then the City reviews your plans to make sure they follow our rules.

These are the City rules that apply to most ADUs. Follow these guidelines to create ADU plans that meet City codes. 

You can also contact the City to answer questions about your project.

Common limitations for single-family homes

• ADUs must be a minimum of 220 sq ft and have a minimum 7.5 ft ceiling heights
• In most residential neighborhoods, you must provide private open space for your ADU
• You must provide adequate natural light and ventilation to the unit
• Your ADU must meet fire safety requirements for safe entry and exits

For multi-family homes with 3 or more units, you may be required to add a fire alarm and sprinkler system to your ground floor.

These requirements can significantly increase the construction and building costs of your ADU.

Number of ADUs you can build at your property

If your property currently has 4 or fewer units, you can build one ADU.

If your property currently has 5 or more units, you can build an unlimited number of ADUs.

If you are doing a seismic retrofit, you can build an unlimited number of ADUs regardless of the existing units on your property.

Rent Control

All multi-family buildings require a waiver to add an ADU, and the units will most likely be subject to Rent Control.

If your lot or existing buildings do not allow you to build an ADU to these requirements, you can apply for a waiver. The City grants waivers for natural light and open space requirements.

All requirements for ceiling height, ventilation, fire safety, and exits must be met.

Waivers trigger Rent Control on the new unit.

Unit and property requirements

Building an ADU may change your occupancy codes

Studios have specific requirements

Take space from existing units

Green Building requirements

Structural work

Add a new building to my lot

Change a free-standing garage or outbuilding

Expand or raise my building

Building an ADU may change your occupancy codes

Architects, contractors, and City inspectors use rules defined by the International Building Code to make sure our buildings are safe.

These rules define the occupancy codes of our homes and buildings. Each occupancy code has different requirements.

• R-2 is the occupancy code for residential buildings with 3 or more units.
• R-3 is the occupancy code for a single-family home or a building with 2 or fewer units.

If you have a single-family home and are adding 1 unit, your property will remain an R-3.

If you have a duplex or a 2-unit building and you are adding 1  unit, your property will change from an R-3 occupancy to an R-2. 

In San Francisco, the Fire Department is responsible for R-2 buildings. So there are additional fire safety rules you will have to follow if you are adding a unit to a 2-unit building. We will take you through these requirements in the Fire Safety section.
 

Studios have specific requirements

If your ADU will be a studio unit (also called an efficiency dwelling unit), it must follow all of the other requirements. It also must have:

• A living room with a minimum 220 sq ft of floor area (and an additional 100 sq ft for each occupant more than 2)
• A closet
• A kitchen area with a sink, cooking appliance, fridge, and counter at least 30 inches wide
• A separate bathroom with toilet and bathtub or shower

In a studio, the floor area of the entire living and sleeping space is the basis for the light and ventilation requirements.

Example: A 250-sq ft studio requires 20 sq ft of window glazing and 10 sq ft of ventilation.

If a bedroom is not fully enclosed, the adjacent room can count towards the light and ventilation requirements. The shared wall must be 50% open and unobstructed. The area must be at least 25 sq ft or 10% of the floor area of the room served.

Take space from existing units

ADUs are commonly built in the garage or storage space of a single-family home.

Up to 25% of an existing unit’s ground floor or basement space can also be converted.

Green Building requirements

All construction in San Francisco must follow state and local law for energy-efficient buildings. Your construction will need an energy inspection as well as other building inspections to verify that your electrical, mechanical, and plumbing work meets the code.

If you are converting more than 1,000 sq ft into habitable space, consult with a Green Building Compliance Professional of Record to certify that your project follows the requirements on the Green Building Residential Alterations form.

All R-3 buildings and R-2 buildings that have 3 or fewer stories must follow the requirements in M-03.

R-2 buildings with more than 3 stories follow the requirements in M-04.

Structural work

You will need to provide structural drawings and calculations created by a structural engineer if:

• Your property is under the Soft Story Ordinance
• You’re doing structural work that will change your building’s gravity load carrying elements
• You’re doing voluntary seismic upgrades

Add a new building to my lot

You can build a new building on your lot as long as you keep the required setbacks and rear yards of your zone.

Use Symbium to measure your lot and determine if this is possible.

Change a free-standing garage or outbuilding

For a free-standing garage or outbuilding, your ADU must follow the rules above as well as these specific building requirements:

• Maximum height: 35 ft
• New unit square footage: 220 sq ft to 1,200 sq ft
• Front setback: determined by your neighbors’ average setbacks
• Side setback: 3 ft

Expand or raise my building

Most ADUs are built within the existing envelope of a building. If you are expanding your building, you are required to post a neighborhood notice and do a design review.

If your new building height will be over 40 ft, the City will need to do a shadow analysis.