Placentia, CA Accessory Structures: ADU Rules (2026)

Chapter 23.73 of the Placentia Municipal Code treats an accessory dwelling unit as a ministerial approval, not a discretionary one. Section 23.73.040 allows an ADU attached to or inside the primary dwelling, or detached on the same lot, in any single family, multi-family or mixed-use zone and in specific plan areas that allow residential uses. A junior accessory dwelling unit is permitted only in a single-family zone.

Section 23.73.060 sets the standards. The ADU follows the underlying zone's setbacks, height and lot coverage unless the chapter or state law says otherwise. An attached ADU cannot exceed 50 percent of the existing primary dwelling; when the primary dwelling is new construction, an attached ADU is capped at 850 square feet for a zero- to one-bedroom unit and 1,000 square feet for a unit with two or more bedrooms. A detached ADU is capped at 1,200 square feet. Side and rear yard setbacks are 4 feet, and a detached unit must sit at least 10 feet from the primary dwelling and every other structure unless that would prohibit an 800 square foot unit.

Height limits are 16 feet for a detached unit, 18 feet within one-half mile walking distance of a major transit stop or on a multi-family multistory lot, and 25 feet or the zone limit, whichever is lower, for an attached unit. One off-street parking space is required, with listed exceptions. Only one exterior entrance is allowed on any one side, utilities go underground, and exterior stairways cannot be clearly visible from an adjacent street.

Under Section 23.73.030 the city decides whether an application is complete within 15 business days, then processes it within 60 days, or 30 days when the plan is preapproved. An applicant can appeal a denial or an incompleteness determination to the planning commission and city council within 5 days.