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Westminster ADUs

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Westminster ADU Guidelines Last Updated 09/20/21

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

Number of ADUs allowed:

a. For lots with an existing or proposed single-family dwelling, one ADU may be on the lot.

b. For lots with an existing multifamily residential dwelling:

i. No more than 25% of the number of the existing units, but at least one unit, shall be permitted as ADUs constructed within the non-livable space (e.g., storage rooms, boiler rooms, hallways, attics, basements, or garages) of the existing multifamily dwelling structure provided that applicable building codes are met; and

ii. Up to 2 detached accessory units.

c. For lots without an existing multifamily residential structure where a new multifamily residential structure is proposed, up to 2 detached ADUs may be on the lot, with separate standards.

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 Accessory Dwelling Unit (ADU)s by ordinance or of the underlying zoning district. ~ AB-68

ADU size:

A. Attached ADUs. The maximum floor area of an attached ADU shall be 1,200 square feet or 50% of the living area of the primary dwelling, whichever is greater.

B. Detached ADUs. 1,200 square feet of floor area.

C. Conversion. An ADU which is converted entirely from within a lawful existing structure is not subject to a maximum floor area requirement. The resultant primary dwelling does need not comply with the minimum floor area requirements of Municipal Code Section 17.210.015, although it must still comply with Building Standards Code requirements relating to minimum floor areas.


a. Setbacks for converted ADUs. No setbacks are required for either: (i) those portions of ADUs that are created by converting existing living area or existing accessory structures to new ADUs; or (ii) constructing new ADUs in the same location and to the same dimensions as an existing structure.

b. Setbacks for non-converted ADUs. For all other ADUs, there must be a minimum of 4 feet of setbacks from side and rear lot lines and comply with all applicable front yard setbacks.

c. Distance between structures on a single-family lot. For a single-family zoned lot, for any detached ADU which is new construction, there must be at least 6 feet between the ADU and the single-family dwelling and all other detached accessory structures.

d. Distance between buildings on a lot with multifamily zoning. For a lot in a multifamily zone, newly constructed detached ADUs must be at least 10 feet from any other dwelling units (other than detached ADUs that are attached to each other) on the property, and at least 6 feet from accessory structures.

e. Public/private easements. No portion of an ADU (whether new construction or converted from existing space) may encroach into any public or private easement such as a utility easement unless the easement holder has provided written permission to construct the ADU in the manner proposed. Roof eaves may not be eliminated to meet the easement requirements. To establish a rebuttable presumption of compliance with these easement requirements, applicants may provide to the city a written declaration, in a form acceptable to the City Attorney, affirming under penalty of perjury compliance with these requirements.


a. In addition to the required parking for the primary unit, one parking space shall be provided unless the ADU has no bedrooms (e.g., a studio), in which case no parking space is required. The required parking space may be provided as:

i. Tandem parking on an existing driveway in a manner that does not encroach onto a public sidewalk and otherwise complies with city parking requirements; or

ii. Within a setback area or as tandem parking unless the Director determines that parking in the setback or tandem parking is not feasible based upon specified site or regional topographical or fire and life safety conditions.

b. Notwithstanding the foregoing, no parking space shall be required for an ADU if:

i. It is located within one-half mile walking distance of public transit;

ii. It is located within an architecturally and historically significant district;

iii. It is part of a proposed or existing primary residence or accessory structure;

iv. When on-street parking permits are required but not offered to the occupant of the ADU; or

v. Where there is a car share vehicle located within one block of the ADU.

When a garage, carport, or covered parking structure is demolished for the purpose of allowing a new ADU, the off-street parking spaces do not have to be replaced.

Fire Safety:

Accessory dwelling units shall not be required to provide fire sprinklers unless they are also required for the primary dwelling. ~ State Standards

Shape, materials and style:

Specific design styles and restrictions are not specified under State Standards. Passageways shall not be required in conjunction with the construction of an accessory dwelling unit. ~ State Standards


ADUs shall not exceed the height of 16 feet unless the units are within the existing space of a single-family dwelling, an accessory structure or multifamily dwelling. ADUs may be permitted on the upper floor of a newly constructed single-family home.

Design review:

The municipality shall provide a ministerial review process which is not based on a discretionary approval for an ADU. The process shall take no less than 120 days. Valid applications submitted for ADUs, if not approved or denied within 120 days from submission, shall be considered approved. ~ State Standards

Number of Bedrooms:

No maximum number of bedrooms is established other than that implied by the maximum size of an ADU allowed. ~ 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:

Connection and utility fees shall be reasonable, and shall not be disproportionately higher than those to develop primary dwellings, so as not to deter the development of ADUs. If a private sewage disposal system is used, such as a septic system, review and approval by a local health officer may be required. ~ State Standards

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. ***

Westminster Municipal Code (WMC) Section 17.210.010 Residential Zoning District Land Uses and Permit Requirements, Table 2-2 Permitted Uses and Permit Requirements For Residential Zoning Districts, indicate that accessory dwelling units (in conjunction with a single-family residence) are permitted by right only in residential zoned districts (R-1 through R-5). In addition, please refer to the following links for WMC Section 17.400.135 & 17.210.015 that pertains to the construction of a ADU.

Residential Building Code:

The California Building Code (CBC) 2019 is adopted.

Read Westminster Housing Market Update

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