Design an ADU that meets City codes

Accessory dwelling units (ADU) must meet City requirements that keep buildings safe and neighborhoods livable.

What to do

After you decide to build an ADU, you must create architectural plans for your ADU. Then we review your plans to make sure they follow our rules.

Follow these guidelines to create ADU plans that meet City codes.

When you must hire a design professional

We require that a licensed design professional sign and stamp most ADU plans.

We do not require a licensed design professional in these cases.

Single-family homes with wood-frame construction (Type V construction) that are less than:

  • 2 stories and basement in height
  • 25 feet wide between bearing walls
  • 25 feet high

Multiple-unit dwellings containing less than 5 dwelling units of wood construction that are less than 2 stories and basement in height.

An unlicensed person cannot design multiple clusters of up to 4 dwelling units.

Read more in Information Sheet G-01.

Common limitations

  • 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 for Local program ADUs.

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

Number of ADUs you can build at your property

Under State Law, you can build 1 ADU or junior ADU (JADU) in single-family homes.

You may build more than 1 ADU in some instances and under our Local program.

If you want to build more than 1 ADU, see more about State and Local ADU programs.

Unit requirements

Entrances and exits

Your ADU must have its own entrance. The person living in your ADU cannot be required to enter through another unit. The units can share a common foyer or hallway.

Most ADUs require two exits for fire safety. The exit path must be 36 inches wide. The clear opening of all doors must be 32 inches wide, which is usually a 34 inch-wide door panel.

Ceiling heights

In hallways and living and sleeping areas, the minimum ceiling height is 7.5 ft. In other rooms (like the bathroom and kitchen), the minimum ceiling height is 7 ft.

Rooms and sleeping areas

Your unit must have:

  • at least one room that’s more than 120 sq ft
  • a designated sleeping are

Habitable rooms, like living rooms and bedrooms, must be:

  • at least 70 sq ft
  • at least 7 ft in any dimension

Kitchens must have a passageway of at least 3 ft between the counters and the wall and a 4-burner stove.

Natural light 

All living spaces in the City must have natural light, also called exposure. The City uses the term glazing to refer to glass in windows, doors, or other fixed openings that let natural light into a building.

State-law ADUs may not have to follow all of these requirements.

Your ADU must also have a window or other glazing that:

  • Is in a bedroom or living room that is 120 sq. ft. or larger
  • Is either greater than 10 sq. ft. or 1/12 of the size of the room size 
  • At least 7.5 inches from the finished floor

The window or other glazing must face a code-compliant rear yard, street (minimum 20 feet in width), or open area that is 25 feet by 25 feet on the ground floor and expands at subsequent floors. 

The Zoning Administrator is may reduce the exposure requirement for an ADU through a waiver so that qualifying windows may face an open area that is no less than 225 square feet in size, has no horizontal dimension less than 9 feet, and is open to the sky with exception of permitted obstructions outlined in Section 140 of the Planning Code. Any exposure that is less than these dimensions will require the approval of a variance.

Habitable rooms, excluding kitchens, home offices and media rooms, must have glazing that’s at least 8% of the floor area. 

Example: if the living room is 90 sq ft, it must have 7.2 sq ft of glazing from a window, fixed opening, or glass door.

Note: See the Fire Safety section for more requirements about windows.

Ventilation

Habitable rooms must have natural ventilation that’s at least 4% of the floor area. An exterior door also counts for the ventilation requirement. If that’s not possible, you must provide a mechanical ventilation system.

Example: A 150 sq ft-bedroom must have a minimum of 6 sq ft of window that can be opened for ventilation. 

All bathrooms must have an exhaust fan.

Utilities

Water: Single-family homes adding an ADU do not usually need additional water capacity. If you are remodeling the primary unit as well, there may be additional water capacity costs. If you are adding 1 unit to a 2-unit building, you may be required to add a sprinkler system to comply with fire safety. This will likely require additional water capacity.

Electric: ADUs require their own electrical service with a dedicated electrical meter, circuit panel, and shut-off. 

Gas: If the ADU has gas appliances, the property's gas lines will need to be extended to the new unit. Gas meter installation must be coordinated with Pacific Gas and Electric.

Meters: all gas and electric meters must meet PG&E requirements. If the meter box is in the exit passageway, it must be in 1-hour fire rated and it cannot block the minimum width of the exit passageway.

Property requirements

Parking

Additional parking is not required for an ADU.

Front setbacks

At least half of the required front setback must be permeable and at least 20% of it must be unpaved and landscaped with plant material.

Side and rear setbacks

Determined by fire safety and zoning requirements

Garbage totes

The City requires garbage, recycling, and compost bins (“toters”) to be stored so that they’re not visible from the street or in an exit passageway. 

Make sure your plans show where your toters will be stored. If they’re not stored inside, make a screened outdoor area (preferably in the rear yard not directly facing a unit's window). You are generally required to have three 32-gallon toters for a single-family home adding one unit.

Open space and rear yards

In neighborhoods zoned for single-family homes (called RH-1 or RH-1 (D) by the City code), the requirements are:

  • Private open space (like a private deck) must be at least 300 sq ft per unit OR 400 sq ft of shared open space per unit.
  • 30% of the total lot depth must remain open in the rear yard.
  • The rear yard may not be less than 15 ft.

In other districts, the requirements are:

  • Open space requirements range from 36 to 125 sq ft per unit.
  • 25 to 45% of the total lot depth must remain open in the rear yard (depending on your neighbors’ rear yards).
  • The rear yard may not be less than 15 ft.

Use Symbium to measure your rear yard.

Fire safety

The City makes sure all construction keeps our residents safe. One effective way to do that is to make sure that if fires start, they can’t spread. These rules keep our buildings and City safe.

Construction

Walls that separate the ADU from a garage or an existing unit and walls on the property line must be 1-hour fire rated. 

New openings within 10 ft of a fire escape or exterior stairs must be fire-rated.

All doors in exit passageways and emergency escape and rescue enclosures must be 1-hour fire rated.

Windows that open into an exit passageway must meet fire-resistance requirements.

If your building has more than 3 existing units, is more than 2 stories, and is made with an unprotected wood frame (type VB construction), new ADUs on the first floor must be built with a protected wood frame, also called type VA construction.

Rescue openings

Every bedroom or sleeping area must have a rescue opening. This can be a door or a window ideally that leads to the public way. The window must:

  • Be at least 5.7 sq ft
  • Be at least 24 inches high and 20 inches wide
  • Be less than 44 inches above the floor
  • Open freely so someone can climb out without keys or tools to open

Exit passageways

The farthest point in the unit to the public way must be less than 125 ft.

The exits and egress paths to the new units also must use protected wood frame construction, also called VA.

Smoke and carbon monoxide detectors

Smoke detectors, also called smoke alarms, and carbon monoxide detectors are required in every residential building. They are required:

  • in the hallway outside a sleeping area
  • in each sleeping area
  • on every floor even if there isn’t a sleeping area

They can be installed after construction and do not need to be included on the plans prepared for the City.

Fire alarms and sprinklers 

A fire alarm is not a smoke detector. It can be manually or automatically activated. The alarm is much louder than a smoke detector and often has a visual light to notify residents of an active fire.

You may be required to install a manual fire alarm system throughout the building and sprinklers on the ground floor of the building if:

  • Your building has 3 or more units and
  • A sleeping room faces the rear yard and
  • Your rear yard is less than 50 ft deep

If your project requires fire alarms or sprinklers, they must be noted on the plans prepared for the City.

If you are uncertain if this applies to your project, check with the Fire Department.

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.

Taking space from existing units

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

Under the Local program, up to 25% of an existing unit’s ground floor or basement’s habitable space can also be converted. A Zoning Administrator can authorize a larger conversion.

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.

Fill out the Green Energy form for your project.

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

Adding 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.

Changing 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: 16 ft
  • New unit square footage: 220 sq ft to 1,000 sq ft
  • Exterior entrance required

See complete rules in the State-mandated ADU program fact sheet (PDF).

Expanding my building

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

Get help

Last updated March 04, 2021