State law permits ADUs up to 1,200 sqft for detached units. 5,000–7,000 sqft typical residential lots. Some older neighborhoods near downtown have slightly smaller parcels. No minimum lot size required by state law to build an ADU.
Up to 16 feet for single-story detached ADUs. Up to 25 feet for two-story ADUs per state law (AB 1332) in qualifying residential zones.
4-foot minimum from rear and side property lines for new detached ADUs. Conversions of existing structures are exempt from setback requirements.
One parking space per ADU may be required. Exempt if within 0.5 miles of public transit, within one block of a car-share vehicle, or if the ADU is a conversion of existing space.
No owner-occupancy requirement for ADUs (made permanent by AB 976 in 2025).
Estimated cost $250K–$375K. Permit fees $5K–$10K. Impact fees: Waived under 750 sqft.
Placentia — branded as "A Pleasant Place to Live" — is a well-established city of approximately 52,000 residents in north-central Orange County. The city features a mix of mid-century neighborhoods with mature tree canopy and newer developments, all served by the highly rated Placentia-Yorba Linda Unified School District. Placentia's historic downtown along Santa Fe Avenue is undergoing a revitalization that includes new dining, retail, and mixed-use development, bringing renewed energy to the city center. The proximity to Cal State Fullerton (CSUF) — located just across the border in Fullerton — creates consistent demand for rental housing from students, faculty, and university staff. Residential lots typically range from 5,000 to 7,000 sqft, providing practical space for ADU construction. The city's central north OC location offers convenient access to the 57 and 91 freeways.