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(510) 330-2387 ext: 190
Schedule ADU Consultation (510) 330-2387 ext: 190

Union City ADUs

Everything about building Accessory Dwelling Units in Union City, CA

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The city government of Union City will approve ADUs under California's statewide mandated regulations.
The California Building Code (CBC) 2019 is adopted.

Last Updated 01/26/21


City Hint: The city permitted a total of 12 ADU projects in the past year of 2019, which is below the average compared to other cities in California.

Number of ADUs allowed:

According to state law, all single-family homes are allowed at least one Accessory Dwelling Unit (ADU). Additionally, single-family lots which are owner-occupied may create one Accessory Dwelling Unit (ADU) and one Junior ADU. Also, multi-family lots may now add one ADU per every four existing residential units, so long as they were legally established.

Types of ADUs allowed:

Detached ADU, Attached ADU, Junior ADU are permitted. ADUs may be new construction or converted from existing space. JADUs must be converted from existing space.

Lot size:

Residential properties will not be subject to any minimum lot size for ADUs by ordinance or of the underlying zoning district. ~ AB68

ADU size:

Residential properties will be approved to build up to 850 sqft for a one bed ADU or up to 1,000 sqft for a two bed ADU, regardless of the underlying zoning standards of the property. A Junior Accessort Dwelling Unit (JADU) is approved up to 500 sqft. According to California Residential Code, the minimum size of any living unit is 150 sqft (including Accessory Dwelling Unit (ADU)s and Junior Accessort Dwelling Unit (JADU)s). ~ Updated: State Law AB-68


The maximum required setback for a detached new construction Accessory Dwelling Unit shall be no more than 4 ft from the rear and side property lines. Setbacks will not be required for Accessory Dwelling Units and Junior Accessory Dwelling Unit (JADU)s converted from existing space that was legally eastablished. Attached Accessory Dwelling Units and conversions from existing space to be expanded will be required to comply with the setbacks of the underlying zone. ~ Updated: State Law AB-68


Replacement parking shall not apply to parcels which convert an existing garage to an Accessory Dwelling Unit (ADU) or JADU. ~ AB68

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.


Owner-occupancy will not be required for new Accessory Dwelling Units (conversion and new construction) built between 2020 and 2025. ~ SB-13

Utility connections:

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

Allowed Zones:

*** Beginning in 2020, according to state law, all residential zoning districts, including single-family and multi-family, are allowed to build Accessory Dwelling Units. ***

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).

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) 2019 is adopted.

Union City City Planning Offices

Union City Planning Department

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

Read Union City Housing Market Update

Call/Text ADU Operator (510) 330-2387
Dial Ext: 190
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ADU Design Library

Browse hundreds of models to find the right fit for your property.

ADU Model 150 sqft

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ADU Model 700 sqft

W 35 ft L 20 ft

ADU Model 1000 sqft

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Customer Reviews

"Housable has been a great resource regarding my ADU project. I purchased both the Property and Design Reports. In both cases, they delivered as promised and on time."

Ed in Corona, CA

"My experience with Housable was exceptional. The team was extremely helpful and responsive. I am very satisfied and happy to have used these services. As a home owner I do not know the construction lingo or process but the Housable team very kind and helpful and patient with me. My expectations were exceeded. Thank you for everything."

Monica H. in Oakland, CA

"The property report was great! Made me feel like my project is feasible."

Alexandria in Santa Ana, CA

Complete 5-Step Process

Browse hundreds of permit-ready ADU designs and order one to customize to your needs.
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What our customers say:

Customer Reviews

"My permits were APPROVED, thank you for all your hard work. I am in the process of meeting with contractors. "

Mary S. in San Jose, CA

"I just wanted to let you know that the permit process has been completed and we are currently in the construction phase. The work you guys did was great and I will definitely be using this service again in the future. I will keep you guys updated on anything important. Thanks!"

Patrick L. in Orange County, CA

Detached ADU - Completed in 2020
1,003 sq. ft., 3 bed, 2 bath

Estimate Your ADU Potential
Costs / ROI



* upon completion of ADU


* based on local average price per sqft


* estimated by location


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


Size: 500 sqft


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)

Check your property's zoning, browse designs & get contractor estimates for your ADU project:

Everything you need to get accurate estimates from contractors for your ADU project. Get help with ADU feasibility, design, permitting and sourcing contractors for your project in one place.

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