STATEWIDE UPDATE: New California ADU Bills SB13, AB68, AB881, AB670 have passed. These laws will create more options for building an ADU in Union City in 2020. To prepare for the upcoming changes use our ADU Services to learn how these laws will effect your property!
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Last Updated 08/11/19


The city government of Union City will approve ADUs under California's statewide mandated regulations.
The California Building Code (CBC) 2016 is adopted with the following amendment(s): 827-16, 822-16 to 832-16 CALGreen
Relevant state bill updates for SB13, AB68, AB881, AB670 are shown in green below.


City Hint: The city has not yet responded to requests for ADU permit volumes for the past year, but they will be provided here once response has been received.


Number of ADUs allowed:

One ADU per one primary dwelling.

AB68 & AB881 Update: Properties which convert existing space to create ADUs may be eligible for one ADU -AND- one JADU.

Types of ADUs allowed:

Accessory dwelling units may be attached, detached, or located above a detached garage.

There are several ways to establish an accessory dwelling unit, which include:
 Conversion of existing floor space within an existing single-family residence;
 Addition to an existing single-family residence;
 Conversion of an existing accessory structure;
 Construction of a new detached ADU; or
 Construction of a new principal dwelling.

Lot size:

Per state minimum requirements.

AB68 & AB881 Update: Properties will not be subject to minimum lot standards by ordinance or of the applicable zoning district.

ADU size:

 The floor area must be between 275 and 640 square feet with a maximum of one bedroom unless the lot is greater than 8,500 square feet in area.  On lots greater than 8,500 square feet, the maximum floor area of an accessory unit is 800 square feet and a maximum of two bedrooms may be allowed.  If the accessory unit is created by converting space within an existing single-family residence, the unit cannot contain more than 25% of the floor area of the principal dwelling.

AB68 & AB881 Update: Properties will be allowed up to 850 square feet for a one bedroom or up to 1,000 square feet for a two bedroom ADU.


Accessory units shall conform to the same setbacks as required for the principal dwelling unless: Located above a detached garage.  If detached, the accessory unit must be located at least feet from the principal dwelling.  If located above a detached garage, the accessory unit must maintain a minimum 5-foot interior side yard setback, 5-foot rear yard setback, and 20-foot street side yard setback if located on a corner lot.

AB68 & AB881 Update: The maximum required setback for a detached new construction ADU shall be no more than 4 feet from the rear or side property lines.


Per state minimum requirements.

AB68 & AB881 Update: Properties which convert an existing garage will not be subject to replacement parking requirements.

Fire Safety:

Per state minimum requirements.

Shape, materials and style:

Accessory units must be clearly subordinate to the main house in terms of size, location and appearance.
 The exterior appearance and character of the accessory unit shall reflect that of the main house.
 Outside stairways must meet setback standards and shall not be visible from the public street.
 If a manufactured home is proposed as an accessory unit, it must be identical to the main house in terms of siding and roof materials, roof pitch, roof eaves and color.


Detached accessory units are limited to one story unless the ADU will be added over a garage consistent with state law.

Design review:

 Attached accessory unit: A building permit is required if the accessory unit is proposed to be attached to the main house, located on the ground floor, and complies with all applicable requirements. Administrative Site Development Review approval by the Planning Division is required prior to building permit issuance if the accessory unit is proposed as a second-story addition or as part of a new principal dwelling.
 Detached accessory unit: Administrative Site Development Review approval by the Planning Division is required prior to building permit issuance if the accessory unit is proposed as a detached structure.

Number of Bedrooms:

Not specified by State Standards.


Both the principal dwelling (main house) and accessory dwelling unit may be occupied as separate single-family dwellings.

SB13 Update: Owner-occupancy requirements for ADUs will be voided statewide for 5 years.

Utility connections:

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

Permit Fees

SB13 Update: Local impact fees for ADUs will be reduced substantially statewide.

Allowed Zones:

ADUs are permitted on single family lots with one dwelling and multi-family lots with one dwelling. Modular/manufactured units are allowed, as long as they meet all City requirements (Planning and Building).

AB68 & AB881 Update: ADUs will be allowed statewide in all single-family or multi-family zoning districts.

Kitchen / Bath:

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

Residential Building Code:

The California Building Code (CBC) 2016 is adopted with the following amendment(s): 827-16, 822-16 to 832-16 CALGreen

Union City City Planning Offices

Union City Planning Department

34009 Alvarado-Niles Road Union City, CA 94587 Union City, CA 94587

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American Mortgage Management

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"The most beneficial service provided was calling the city on my behalf. This saved me a significant amount of time because I am rarely able to get someone from the city on the phone, nor do they return calls. I usually have to visit the permit offices."

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Costs / ROI


* upon completion of ADU


* based on local average price per sqft


* estimated by location


* 30 years / 5% interest rate / 20% down payment


Appreciation Estimate = (Base Value: $) / (Home's Living Space: sqft) * (ADU's Living Space: sqft)

Rental Estimate = (Rent Per Sqft: $3.68) * (ADU's Living Space: sqft)

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