Are you looking to add an apartment, or a second house on your property? Are you looking for additional rental income? Do you want to increase the value of your property? You may want to consider taking advantage of the change in State law that allows you to add a second house, called an Accessory Dwelling Unit (ADU), to your property. More information can be found on San Diego County Planning and Development Services website.

What is an Accessory Dwelling Unit (ADU)?

An ADU is an attached or a detached residential dwelling unit which provides complete independent living facilities for one or more persons. Essentially, ADU’s are a unique opportunity to address a variety of housing needs and to provide affordable housing options for family members, friends, students, the elderly, in-home health care providers, the disabled, and others that can be added to a lot that is zoned for, and has an existing residence. ADU’s are often referred to as mother-in-law apartments, granny flats, guest houses, or studio apartments.

ADU’s must be located on the same legal lot as the existing single-family residence, but can have varying configurations. An ADU can be detached (i.e. separate building in a backyard), attached to, or part of the primary residence, or a garage conversion. They shall provide permanent provisions for living, sleeping, eating, cooking, and sanitation. ADU’s are independent from the main residence, with no interiors access to the main residence and cannot be sold separately.

ADUs are independent living units that have their own kitchens, bathrooms, living areas, and entrances. Essentially, it’s an additional living space that can be added to almost any residential property, provided you have adequate space for the additional parking spaces, and septic improvements (if required).

May I sell or rent my ADU?

An ADU cannot be sold separately from the existing single-family residence, but there is no restriction on who may rent the ADU. However, an ADU shall not be used or rented for less than 30 days.

What size ADU is allowed? How big?

An ADU is intended to be secondary in size to the single-family residence. An ADU attached to a primary dwelling may be up to 50% of the size of the single-family residence, up to a maximum of 1,200 square feet. An ADU detached from the single-family residence may be up to 1,200 square feet, regardless of the size of the residence.
Examples for the allowed sizes are provided below:

Square Footage of
Existing single-family residence (SFD)
Detached ADU Maximum Allowed SqFt
Attached ADU
Maximum Allowed SqFt (up to 50% of
1,450 sq. ft. 1,200 sq. ft. 725 sq. ft.
1,800 sq. ft. 1,200 sq. ft. 900 sq. ft.
2,000 sq. ft. 1,200 sq. ft. 1000 sq. ft.
3,000 sq. ft. 1,200 sq. ft. 1,200 sq. ft.
4,500 sq. ft. 1,200 sq. ft. 1,200 sq. ft.

Do I need to provide additional parking for a new ADU?

Although, an ADU shall provide only one parking space, appropriate parking should be considered when designing your ADU. The parking space for the ADU may be located in an existing driveway as tandem parking as long as the required parking space(s) complies with the required front yard and/or exterior side yard setback(s). Alternatively, if an ADU is located within ½ mile from a bus stop, no additional parking is required.

What are the height limitations for the ADU?

A detached ADU is limited to 2 stories and 24’ in height.

Where is an ADU allowed?

An ADU can be located, upon issuance of a building permit, on residentially zoned property that has an existing single-family residence. Only
one ADU is allowed on qualifying parcels. An ADU may not be placed on properties that are zoned and developed with duplexes or other
types of multi-family housing, or on properties that have an existing guest living quarters, accessory living quarters, or accessory apartment. However, an existing guest living quarters, accessory living quarters, or accessory apartment could potentially be converted into an ADU.

May I convert an existing accessory structure into an ADU?

Yes, any permitted existing accessory structure such as a garage, workshop, guest living quarters, accessory living quarters, or accessory apartment, etc. may be converted into an ADU regardless of lot coverage, setbacks regulations.

I want to attach a garage to my detached ADU, is that allowed and how big can the garage be?

Yes, an attached garage is allowed as long as the total floor area of a proposed garage attached to a detached ADU does not exceed the allowable combined square footages per Section 6156.g. If the proposed garage, attached to a detached ADU per Section 6156.g exceeds 1,000 square feet (combined with any other existing accessory structures) or 12’ in height, the garage portion of it has to comply with the main building setbacks. The garage with interior access to the ADU must be designed and used to shelter or storage of vehicles owned, or operated by the occupants of the ADU.
No other rooms, additions, uses, etc. shall be attached to the ADU, unless authorized by an Administrative Permit.

What if I want to convert my garage to an ADU, do I need to replace the parking?

Yes, when converting a garage to an ADU the property must replace the parking spaces being lost by the conversion, in addition to the one parking space required for the new ADU. An existing single-family residence requires at least 2 parking spaces. The replacement parking may be in any configuration including tandem, within the side or rear yard setback areas, or on a driveway, but it cannot be in the front yard or exterior side yard setbacks.

Is a Building Permit required for an ADU?

Yes, you will be required to obtain a Building Permit to ensure that the new living area meets all the zoning, building, health & safety codes.
Please see link below for “How to obtain a building permit”; https://www.sandiegocounty.gov/content/dam/sdc/pds/docs/pds441a.pdf

What are the setbacks for an ADU?

All newly constructed ADU’s must comply with the required main building setbacks. Please contact the appropriate Fire Department ASAP to get the setbacks confirmed and to find out if fire sprinklers are required or not (see link below);

What about utility connections?

ADU’s are required to provide the necessary utility services such as water, sewer or septic. Please check with each service agency to obtain the appropriate information on their requirements including permit processing and fees.

What do I have to do if the ADU is on septic?

If your property is served by a septic system, the size of the septic tank and leach field must be increased to support an ADU. For questions about size and setback requirements, please contact the Department of Environmental Health at 858-565-5173. See link for more information about septic systems: https://www.sandiegocounty.gov/content/sdc/deh/lwqd/lu_septic_systems.html

What are the different Utility Connection Fees?

Depending on the district, lot size, location, etc. new, or separate utility connection fees may be required for an ADU: such as, Traffic Impact fees (TIF), Drainage fees, School fees, Water Dept./Water Connection fees, Sewer fees, etc. Please consult with each service agency early in
your process if you are unsure of the availability and fees.

Is the ADU required to have fire sprinklers?

In some cases an ADU does not require the installation of fire sprinklers but this determination is based upon a variety of factors including the size of the ADU and its distance from a roadway. Prior to investing in a project, owners should discuss their project with the appropriate Fire Department ASAP who will determine the fire protection services that may be required.

How much does it cost to obtain a building permit for an ADU?

It depends. Building Permit fees can be a significant part of the cost of your ADU, and are worth considering during the early phases of your project. Our building permit fee calculator can help you estimate the costs of your ADU, it can be found at Building Forms and Handout page. These costs do not include your consultant fees and other fees charged by other County Departments and/or Agencies. As a rough guide of estimation, the total County mitigation fees are approximately 10% of the construction costs of new ADU’s.

Accessory Dwelling Units – Contacts

For questions regarding ADU’s, or what the development standards are, please see link below: https://www.sandiegocounty.gov/content/dam/sdc/pds/zoning/formfields/PDS-611.pdf