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Mission Viejo ADUs

Everything about building Accessory Dwelling Units in Mission Viejo, CA

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400 sqft

749 sf
1 Bed
The city government of Mission Viejo has updated its local zoning codes to comply with the State ADU mandate.
The California Building Code (CBC) 2019 is adopted.

Last Updated 08/14/21

Number of ADUs allowed:

According to state law, all single-family homes are allowed at least one Accessory Dwelling Unit (ADU). Additionally, single-family properties which are owner-occupied may create one Accessory Dwelling Unit (ADU) and one Junior Accessory Dwelling Unit (JADU). Also, multi-family properties 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 approved. ADUs may be new construction or converted from existing space. Junior ADUs must be converted from existing space.

Lot size:

Residential parcels will not be subject to any minimum lot size for Accessory Dwelling Units by ordinance or of the underlying zoning district. ~ AB-68

ADU size:

Residential lots will be permitted to add 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 ADU is permitted up to 500 sqft. According to California Residential Code, the minimum size of any living unit is 150 sqft (including Accessory Dwelling Units and Junior ADUs). ~ According To AB68


Setbacks for a detached new construction Accessory Dwelling Unit (ADU) shall be no more than 4 ft from the rear and side lot lines. No setbacks shall be required for Accessory Dwelling Unit (ADU)s and Junior Accessory Dwelling Unit (JADU)s converted from legally eastablished existing space. Attached new construction Accessory Dwelling Unit (ADU)s and conversions from existing space to be expanded must comply with the setbacks of the underlying zone. ~ AB68


Replacement parking shall not apply to parcels which convert an existing garage to an Accessory Dwelling Unit or Junior Accessory Dwelling Unit. ~ According To AB68

Fire Safety:

Accessory dwelling units shall not be required to provide fire sprinklers if they are not required for the primary residence and may employ alternative methods for fire protection. (State requirements)

Shape, materials and style:

An additional dwelling unit shall be located only within the rear half of the parcel, and shall not exceed 20 feet or one story in height. The additional dwelling unit shall be architecturally compatible with the design of the main dwelling unit and the surrounding neighborhood in terms of landscaping, scale, height, length, width, bulk, lot coverage, and exterior treatment.


Max ADU height is 20 feet or one story.

Design review:

State Standards don't require any additional design review.

Number of Bedrooms:

Not specified by State Standards.


Between between 2020 and 2025, owner occupancy requirements will not apply to new ADUs. (applicable to new construction and conversion units) ~ SB13 Update

Utility connections:

Local health officer approval where a private sewage disposal system is being used, if required. (State requirements)

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. ***

Allowed zones are R, RPD_14, OS, RPD_6.5, RPD_3.5, RPD_30, R/OS, RPD_30A, RESIDENTIAL-ESTATE.


This section shall not validate any existing illegal "additional" dwelling unit. An application for a permit may be made pursuant to the provisions of this section to convert an illegal "additional" unit to a conforming legal "additional" unit, and the standards and requirements for the conversion shall be the same as for a newly proposed "additional" dwelling unit."

Residential Building Code:

The California Building Code (CBC) 2019 is adopted.

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