Accessory Dwelling Unit (ADU) City Regulations

Are ADUs allowed in Union City:


Number of ADUs allowed:

Limit of one ADU per one primary dwelling structure.

Types of ADUs allowed:

Attached or detached ADUs are permitted.

Lot size:

Must meet state minimum requirements.

ADU size:

On lots less than 8,500 sq. ft., the floor area of an ADU must be between 275 and 640 sq. ft. with no more than one bedroom. Lots greater than 8,500 sq. ft. can feature an ADU with a maximum floor area of 800 sq. ft. and a maximum of two bedrooms. ADUs converted from space within an existing single-family dwelling cannot contain more than 25% of the floor area of the principal structure.


ADUs share the same setback requirements as the principal dwelling unless: located above a detached garage wherein setbacks are 5 feet from interior side yard and rear yard and 20 feet from street side yard if located on a corner lot. Additionally, detached ADUs must be at a distance of 10 feet from the primary dwelling.

Kitchen / Bath:

ADUs must include a complete and independent living facility for sleeping, cooking, and sanitation purposes. A kitchen and bathroom must be permitted for the sole use of the unit.


Refer to state minimum requirements.

Fire Safety:

Refer to state minimum requirements.

Shape, materials and style:

ADUs should be subordinate to the main residence in terms of size, location and appearance and should match exterior appearance and character.


Detached ADUs cannot exceed one story and a maximum height of 12 feet unless a higher roof pitch is needed to match the main house. ADUs located above detached garages must not exceed 30 feet.

Design review:

Design reviews and building permits are required for attached and detached accessory unit.


Both the primary residence and accessory dwelling unit may be occupied as individual single-family dwellings.

Utility connections:

Adequate water and sewer service must be provide to ADU. Separate or combined utilities are allowed.

Permit Fees:

Please refer to  

Allowed Zones:

ADUs are permitted on lots in all single-family residential or multi-family zoning district with an existing single-family home.

Code Link: 

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