Union City has not updated its regulations pursuant to California’s statewide changes enacted January 1, 2020. This is a copy of the most recent version. Follow State guidelines in lieu of the below post.
Number of ADUs allowed:
Limit of one ADU per one primary dwelling structure. Accessory dwelling units shall be permitted in all single-family residential districts and on any lot located within a multifamily residential district that contains an existing permitted single-family home.
Types of ADUs allowed:
Attached or detached ADUs are permitted.
Must meet state minimum requirements.
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.
Attached ADU – must conform to the required front, rear and side yard setbacks of the zoning district in which they are located.
Eaves and Gutters: Eaves and gutters are permitted to encroach eighteen (18) inches into the side and rear yard setbacks, but shall be located no closer than two (2) feet to a property line.
Detached ADU –
1. Accessory structures may be attached to and have a common wall with the main structure on a site; provided, that the accessory structure shall provide the same front, side and rear yards as required for the main structure except that an attached patio cover and/or enclosed patio may encroach into the required rear yard area from the main structure when:
a. There remains at least ten (10) feet of clear, open space from the nearest projection of the patio cover eaves or screening material to the rear property line;
b. The height of the structure at its maximum vertical projection does not exceed twelve (12) feet from grade;
c. Maximum site coverage allowed in the residential zoning district is not exceeded;
d. The attached accessory structure is not used for additional living or sleeping purposes.
2. a. Detached accessory structures over one hundred twenty (120) square feet in building area are subject to administrative site development review approval in accordance with Chapter 18.72. Detached accessory structures over one hundred twenty (120) square feet of building area or over six and one-half (6-1/2) feet in height shall be located not closer than five (5) feet from any other structure, five (5) feet to a side or rear property line. Such structure(s) shall be limited to one (1) story, with a maximum height of twelve (12) feet. Eaves and projections shall meet the standards of the Uniform Building Code.
b. If the total square footage of detached accessory structures exceeds one hundred twenty (120) square feet, then the structure(s) which brings the combined total building coverage above one hundred twenty (120) square feet, and all subsequent structures, shall be subject to administrative site development review approval in accordance with Chapter 18.72.
3. Detached accessory structures shall be located on the rear half of the lot or site and in no case forward of the main structure.
4. On a corner site, detached accessory structures shall have a side street setback of twenty (20) feet (where the rear yard abuts the side yard of a key lot), with a rear yard of five (5) feet, except, where the rear yards of corner lots adjoin the side street, setback may be ten (10) feet in the RM district and fifteen (15) feet in the RS district.
5. On a corner site, garages and carports which are entered perpendicular to and from across the side property line adjoining the street shall be located not closer than twenty (20) feet to such property line.
6. On a lot with double frontage, detached accessory structures shall not be located closer to either street than the front yard as required for the main structure.
7. In all RS and RM districts, detached accessory structures shall not cover more than thirty percent (30%) of the actual rear yard.
No additional setbacks shall be required for conversion of a permitted garage or the portion of a permitted garage converted to an accessory dwelling unit.
Note: Fire Department regulations should be assessed on a project by project basis.
On lots less than 8,500 sq.ft. in area, the ADU shall have no more than one (1) bedroom.
On lots 8,500 sq.ft. in area or more, two (2) bedrooms are allowed.
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.
Note: Drainage and sewer connections should be assessed on a project by project basis.
When off-street parking is provided for an accessory dwelling unit, it shall be accessed from a driveway in common with the primary dwelling in order to prevent new curb cuts, excessive paving, and elimination of street trees, unless separate driveway access is permitted by the Director upon a determination that separate access will result in fewer environmental impacts such as excessive paving, unnecessary grading or unnecessary tree removal, and that such separate access will not create the appearance, from the street, of a lot division or two-family use.
Additionally, when off-street parking is required for a new accessory dwelling unit, such parking shall be fully contained on private property, and shall not overhang into any portion of the public right-of-way, including the sidewalk. Required parking for accessory dwelling units may occur within driveways, on concrete aprons adjacent to driveways, or on other compact material for vehicle parking adjacent to driveways. If a concrete apron is constructed adjacent to an existing driveway to satisfy parking requirements, the entire driveway shall be replaced to appear uniform. A minimum landscaped setback of three (3) feet shall be provided between the driveway and the interior side property line. If front or street side yard landscaping is removed, remaining landscaping shall be upgraded to meet the requirements of Section 18.112 and the Landscape Standards Policy Statement.
Refer to state minimum requirements.
Shape, materials, and style:
a. The unit shall be clearly subordinate to the principal dwelling unit on the parcel by size, location and appearance.
b. The exterior appearance and character shall reflect that of the existing principal dwelling unit in terms of materials and design, including roof materials, roof pitch, roof eaves and overhang, color scheme, trim elements and detailing including window and door frames, and architectural features.
c. Any manufactured home proposed as an accessory dwelling shall be identical in terms of siding and roof materials, roof pitch, roof eaves and color to the principal residential structure on the lot.
d. The structure shall be located and designed so as to not disrupt the privacy of, or create noise impacts on adjacent residents and yards.
e. No fencing shall be permitted above three (3) feet in height within the common area(s) between the principal dwelling and the accessory dwelling unless the fencing is a required safety feature (e.g., fencing around a pool).
f. Any dead, dying or damaged landscaping shall be replaced on the lot.
g. Detached accessory dwelling units shall provide window treatment that includes mullions and decorative window trims.
h. Attached accessory dwelling units shall be painted to match the primary dwelling. In the event an exact match cannot be achieved, the entire structure shall be repainted.
i. If the conversion of an existing garage to an accessory dwelling unit includes the removal of the garage door, then the front façade shall be designed with one (1) or more windows, architectural detailing, trim, colors and materials consistent with the primary dwelling. A minimum of two (2) feet of landscaping and irrigation shall be added between the accessory dwelling unit and the abutting driveway.
j. For properties located in the Landmark and Historic Preservation Overlay Zone, the California Register of Historical Resources, the National Register of Historic Places, or considered a historic resource after completion of a historic resource evaluation, compliance with the appropriate Secretary of the Standards for the Treatment of Historic Properties shall be required, as determined by the Director.
k. The roof of the structure shall not be used as a deck or floor.
Detached ADUs cannot exceed one story and a maximum height of 12 feet.
The unit may be established through: conversion of existing floor space in a single-family structure; a single-story addition to an existing single-family structure; conversion of an existing, permitted detached accessory structure; the construction of a new detached unit as permitted in this section; and construction of a new principal dwelling; or the conversion of an existing garage.
i. An attached accessory dwelling unit shall be located within the area of the lot allowed for principal dwellings by the zoning ordinance and must conform to the required front, rear and side yard setbacks of the zoning district in which they are located.
ii. Detached accessory dwelling units shall be located in the rear half of the property.
iii. No additional setbacks shall be required for conversion of a permitted garage or the portion of a permitted garage converted to an accessory dwelling unit.
Exterior doors to attached and detached accessory dwelling units shall be setback a minimum of ten (10) feet of adjacent property lines, and a covered entry way of not less than three (3) feet deep shall be provided for the accessory dwelling unit.
In no instance shall an exterior door to an attached accessory dwelling unit be located on the same elevation as the entrance to the primary dwelling.
Outside stairways to the accessory dwelling unit shall be allowed subject to the applicable setback standards of the principal dwelling and shall not be visible from the public street.
Rear Yard Coverage:
Accessory dwellings are subject to the lot coverage standards in the zoning district in which they are located.
Design reviews and building permits are required for attached and detached accessory unit.
Note: Historic neighborhoods or districts should be assessed on a project by project basis.
Both the primary residence and accessory dwelling unit may be occupied as individual single-family dwellings.
Adequate water and sewer service must be provided to ADU. Separate or combined utilities are allowed.
ADUs are permitted on lots in all single-family residential or multi-family zoning district with an existing single-family home.
Important Note: Rules and regulations are updated and changed frequently. It’s one of our jobs to be up to speed and navigate those regulations. Let us know if our website isn’t up to date or if you have any information that could help. Cheers!