What's an ADU? FAQs

What's an Accessory Dwelling Unit (ADU)?

ADUs, sometimes called a Second Dwellings, Auxiliary Dwelling Units, Granny Flats, or Mother-in-Law’s Quarters, are a completely self-contained housing unit located on the same lot as another home. ADUs have their own kitchen, bathroom, and living area. ADUs are considered accessory because they are typically smaller than the primary dwelling and are not considered the main use on the lot.

Where can I build an ADU?

ADUs may be constructed on any lot developed with an existing primary dwelling, or on a lot where a primary dwelling will be constructed at the same time as an ADU. An ADU can be attached to the primary dwelling or detached in a freestanding building. ADUs are allowed in the side and rear yards but are not allowed in front yards. In the side and rear yards, the first floor of the ADU must be set back at least four feet from all property lines and from other buildings. The second floor of an ADU cannot be located in the side or rear yard setback.

Is there a maximum size for my ADU?

Detached ADUs may be up to 1,200 square feet of livable space. Attached ADUs may be up to either 1,200 square feet or 50% of the size of the primary dwelling, whichever is less. In any case, you are guaranteed that the ADU may be at least 850 square feet. For example, a 2,000-square-foot house may have an attached ADU of up to 1,000 square feet, or a detached ADU of up to 1,200 square feet.

Can I convert an existing structure to an ADU?

Yes, existing structures such as garages, workshops, guest quarters or portions of a primary dwelling may be converted to an ADU. Some upgrades may be required for structures that were not originally meant to be inhabited in order to meet Building Code requirements.

How much parking does an ADU require?

ADUs do not require any additional parking. Additionally, if a garage or carport serving the primary dwelling is converted into an ADU, no replacement covered parking spaces for the primary dwelling are required.

Can my ADU be more than one story tall?

Yes, ADUs are subject to the same height and story limits set by the Zoning Code for the primary dwelling. In most areas of the City, the maximum height is 35 feet if attached, and 30 feet if detached. In most cases, you can build two stories, but be sure to check with Planning (951-826-5800). ADUs may also be constructed above existing structures such as garages or as second-story additions to the primary dwelling, provided setbacks can be met.

Do I need a permit to build an ADU?

Yes, a building permit will be required. Plans will need to be prepared by a licensed design professional, such as an architect, and submitted for review to the Building & Safety Division. Plan Check and Permit Issuance fees will apply. Check with the Building & Safety Division at 951-826-5697 for more information.

Can I rent or sell my ADU?

An ADU can be rented separately from the primary dwelling. The property owner does not have to occupy one of the homes on the property to rent either home to other occupants. An ADU cannot be sold or conveyed separately from the primary dwelling except in limited circumstances by nonprofit affordable housing organizations.

How do I connect my ADU to utilities?

ADUs may have their own separate water, electricity, gas, sewer and telecommunications connections, or may be tied into the existing services for the primary dwelling. Separate connections allow the ADU to be billed separately but cost more to install. Contact Riverside Public Utilities at 951-826-5489 (Electric) or 951-826-5285 (Water), or the Public Works Department at 951-826-5341 (Sewer), for more information. Gas and
telecommunications questions will need to be directed to the private provider in your area. In some areas of the City, electric and/or water service is provided by other agencies.

What are the fees involved in building an ADU?

In addition to Plan Check and Permit Issuance fees, ADUs are subject to some – but not all – of the development impact and utility connection capacity fees that primary dwellings are. Total fees will depend on the specifics of your property and project. Contact the Building & Safety Division at 951-826-5697 for questions regarding fees.

Is there financial assistance to build an ADU?

The City does not offer financial assistance, but the State may have grants of up to $25,000. You can find additional information at: https://www.calhfa.ca.gov/adu/index.htm