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All ADU Regulations

Palo Alto, California

Palo Alto has updated its ADU ordinance to comply with new state laws for 2020. Below are the up-to-date requirements for permitting an ADU in Palo Alto.
Updated May 09, 2023
The city of Palo Alto is a hub for technological innovation, surrounded by beautiful residential suburbs and historic architecture.
Adding an ADU to your property is a great way to increase the value of your home and also earn an additional source of monthly income. The city has revised its ADU ordinance as of 2020 to comply with new state laws. Here are the up-to-date requirements for permitting an ADU in Palo Alto.

General ADU requirements

The requirements of your project would change based on the type of ADU you’re building. Detached, attached, conversion, and Junior ADUs (JADUs) should match the design of the primary dwelling and keep roof forms, materials, and other architectural details similar.
Typically, ADUs must be equipped for independent living and have permanent facilities for:
  • Living
  • Eating
  • Sleeping
  • Sanitation
  • Cooking
  • Exterior access that is separate from the primary dwelling

Regulating bodies

The regulations for building an ADU in Palo Alto are determined by two governing bodies, the state government, and the local authority, and the applicability of these codes depends on the type of unit you’re building.
Units governed by the State Code are:
  • An ADU and JADU within the existing space of a single-family dwelling or an ADU within the existing space of an accessory structure (i.e. conversion without substantial addition)
  • An ADU and JADU within the proposed space of a single-family dwelling
  • A newly constructed detached ADU on a lot with a proposed or existing single-family dwelling, provided the ADU does not exceed 800 sq. ft., 16 ft. in height, or 4 ft. side and rear (i.e. interior) setbacks
  • ADUs created by conversion of non-livable areas within existing multi-family dwellings
  • Up to two detached ADUs on a lot with an existing multi-family dwelling
In all other cases, local regulations apply when building an ADU in Palo Alto.


Before you obtain a permit for your proposed ADU, you need to assign a street address by the planning department.
In the case of a JADU, a Deed Restriction will need to be recorded with the County prior to permitting. A deed restriction limits what an owner can do on their property including what they can build. Deed restrictions typically do not expire, unless an expiration date is outlined in the document.
If your property is listed on Palo Alto’s historical inventory, the California Register, or the National Register of Historic Places, and you plan to build an ADU or a JADU, you must comply with the Secretary of the Interior’s Standards for the treatment of historic properties.
If you remove any trees to make space for the ADU, you must replace them according to the Tree Technical Manual requirements.
ADUs and JADUs may not be sold separately from the primary residence.


Generally, fees make up about 10% of your total project cost. While there are many small fees associated with building an ADU, the main ones you’ll encounter are Plan check fees, Permitting fees, and Impact fees.
Plan check fees include the cost of assembling and submitting your ADU plans for approval and are 75% of the cost of your building permit fees. They also cover the cost of zoning clearance and address assignment, which can cost up to $500-$600 each. Once a plan check is submitted, building permit fees are paid to review whether your project is safe, legal, and possible. The plan check can be up to approximately 1.5% of your project’s construction value.
Impact fees cover the cost of public services provided by the government, like housing, library, park, and public safety facilities. Most impact fees are not applicable for ADUs under 750 sq. ft., but if your ADU is larger than 750 sq. ft., you’d have to pay an amount proportional to the size of the primary dwelling. As of 2023, school Impact fees are currently $4.79 per sq. ft. and Traffic Impact fees can cost roughly $1,600 per unit.


All properties with the following zoning codes are eligible for ADUs:
  • R-1 (most single-family residences)
  • R-2, R-E, R-M, RMD (two-family residences, residential estates, single- and two-unit multi-family residences)
  • OS (open space) when single-family residential is a permitted land use:
  • PC (planned community when single-family residential is a permitted land use:
To build an ADU on your property, you must have an existing or proposed single-family home or an existing multi-family building, such as a duplex or a triplex.

Access points

ADUs are meant to be independent, so attached ADUs may not have an interior access point or other entryways that connects to the primary dwelling. On the other hand, since JADUs may share bathroom/sanitation facilities with the primary dwelling, they must have an interior access point for convenience.
Unless your home is on a corner lot, your ADU and your main dwelling may not have entranceways that face the same lot line. The exception to this rule is if your ADU is located in the rear half of your lot.
If you have an attached ADU on the second floor of your main dwelling, any exterior staircases should be located toward the interior of the lot or rear yard of the property.


Since ADUs are meant to be self-sufficient, they must have a kitchen equipped with:
  • A sink with hot and cold water
  • A countertop for food preparation measuring at least 24 in x 36 in
  • A refrigerator/freezer combination of at least 16 cubic foot (CF).
  • An oven or microwave
  • A range with a minimum of two burners
While most of the above requirements apply to JADUs as well, JADUs may have a smaller refrigerator/freezer combination of 10 cubic foot (CF) instead.

Number of units

If your lot is zoned for an existing or proposed single-family home, you may have one ADU and one Junior ADU (JADU). In the case of multi-family homes, the number of ADUs you’re allowed to add depends on the type of ADU you’re building and the number of dwelling units already on your property. Typically, multi-family dwellings can have up to two detached ADUs and have conversion ADUs up to 25% of the number of dwellings units.

Building size

The minimum size for both ADUs and JADUs is 150 sq. ft. The maximum size you can build differs under certain conditions.
For detached ADUs in single-family units under the State code, 800 sq. ft. is the size limit.
Local requirements stipulate that the maximum is 900 sq. ft. or 1,000 sq. ft for ADUs with two or more bedrooms. However, if an ADU is attached to a single-family home, it may not exceed 50% of the size of the primary dwelling. The maximum size for JADUs is 500 sq. ft., as described by local regulations.

Building height

Detached ADUs under State Code can reach a maximum height of 16 ft. Attached ADUs can reach the same height as the main structure, assuming they comply with the underlying zoning district’s setbacks, including daylight plane requirements.
Under local regulations, ADUs have different height limits:
  • ADUs in R-E district can reach up to 30 ft and ADUs in OS zone can be built up to 25 ft.
  • Units built in a flood zone are not entitled to any height extensions granted to the primary dwelling
  • Attached ADUs in R-E and OS districts may have two stories, and all other zones are only allowed one. All detached ADUs should be single-story dwellings


Basement space can be used for an ADU in the R-1 zoning district (and subdistricts). The square footage will not be included in the calculation of floor area for the entire site, as long as the measurement from the first finished floor to grade around the perimeter of the building is no more than 3 feet.


Minimum setbacks of 4 ft. from the side and rear lot lines, as well as 6 ft. from any existing structures, are required for detached ADUs. Attached ADUs may be required to have 6 ft. setbacks from side and rear lot lines.
Detached ADUs should maintain distances of 3 ft. from the exterior walls of the primary dwelling.
While roof eaves may encroach up to 2 ft. into the setbacks, windows, doors, other projections, basements, and other below-ground structures may not do so.

Fire safety

You may install fire sprinklers on the property only if they are required for the primary dwelling. However, you need to ensure the new structures comply with the California Fire Code.


Replacement parking is not required when a parking space is converted to an ADU or is demolished to build an ADU.
Replacement parking is required if an attached garage is converted to a JADU. Parking can be an uncovered space anywhere in the lot within the front or street side yard setback for the property. Modification of this space is subject to the discretion of relevant authorities.
The maximum size of a covered parking space for an ADU is 220 sq. ft. This area shall count toward the total floor area of the site, but it will not add to the size of the ADU unless it’s an attached ADU.
The ADU should have street access to parking from the same driveway as the primary dwelling to prevent new curb cuts, excessive paving, and cutting down of street trees. You can build a separate driveway if it causes less environmental impact.


The following regulations are in the interest of privacy for both you and your neighbors:
  • Doors and decks on the second story may not face a neighboring residence
  • Decks and balconies should use a non-transparent screening wall or a similar installation so you cannot see into neighboring properties
  • Second-story windows have to be offset from neighbor’s windows to maximize privacy
  • Second-story windows should have a 5 ft. sill height or may use glazed panes at points where they face adjacent properties


Owner occupancy is not a requirement for permitting an ADU from January 1, 2020, until January 1, 2025. This is a great opportunity for rental property owners to increase their yields in a cost-effective way.
Outside of this period, in properties with a JADU, the owner must reside in either the JADU or the primary dwelling. Owner-occupancy is not required if the owner is a governmental agency, land trust, or housing organization.


While long-term rentals are permitted for ADUs, short-term rentals of less than 30 days (e.g. Airbnb) are not permitted in Palo Alto. The owner may also rent out both their primary residence or the ADU.

Special Considerations

Every property is unique, which means building your ADU while adhering to all these regulations is no easy task. We can customize an ADU to fit both your requirements and the local regulations, without compromising the quality and elegance of the new addition to your home.
Do you have a utility easement over your property? Are you on a lot with special setbacks? A custom ADU might be right for you. Reach out to us and we’ll help you build a custom ADU to fit your unique property characteristics and local regulations!


What is the ADU rule in Palo Alto?

In the City of Palo Alto, an ADU can either be a conversion of an area within an existing structure or a hybrid project such as detached ADUs that add surface area to an existing site.

What is the size limit for an ADU in Palo Alto?

The size limit of an ADU depends on the type of ADU and the number of bedrooms. If governed by Local codes, an attached ADU with just one bedroom/studio layout may be 900 sq. ft., or 1,000 sq. ft. if it contains more than one bedroom. On the other hand, detached ADUs under the State code may be up to 800 sq. ft.

What is the difference between an ADU and JADU?

A JADU, or Junior ADU, is a smaller ADU that is contained within an existing primary dwelling. They may be up to 500 sq. ft. and may share sanitation facilities with the primary dwelling, as long as they have interior access to the shared facilities.

How close to my house can I build an ADU?

You may build a detached ADU ten feet away from your primary dwelling, provided it is setback 5 ft. from property lines.

How much is the Palo Alto ADU impact fee?

Impact fees can be broken down into a few categories. Typically, ADUs under 750 sq. ft. are exempt from some fees like Park Impact fees and Library Impact fees, but all residences must pay Housing Impact fees of approximately $20-$25 per sq. ft.
School Impact fees also vary based on square footage and, as of 2023, the current rate is $4.79 per sq. ft. Traffic Impact fees can run you about $1,600 per unit.

Want to learn more about ADU regulations in your area?

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