ADU rules in San Diego County, CA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
In unincorporated San Diego County, one ADU and one JADU may be added to a lot with an existing or proposed single-family dwelling. A detached ADU may not exceed 1,200 sq ft; an attached ADU is capped at 50% of the main home, up to 1,200 sq ft. Rules implement California ADU law.
San Diego County regulates ADUs in unincorporated areas through Section 6156 of the Zoning Ordinance, applying the framework set by California ADU law (Gov. Code 66310-66342). Per the County's PDS-611 handout, a lot with an existing or proposed single-family dwelling in a residential or mixed-use zone may add one ADU and one JADU. A detached ADU may not exceed 1,200 square feet, independent of the size of the main home. An attached ADU may not exceed 50% of the floor area of the single-family dwelling, up to a maximum of 1,200 square feet. A detached ADU is limited to 25 feet in height (except in multifamily complexes). Newly constructed ADUs must meet the required front-yard setback and a minimum side and rear setback of at least 4 feet (except fire setbacks); an ADU of 800 sq ft or smaller may encroach into the front-yard setback where backyard placement is infeasible. One parking space is required, which may sit in a setback or in an existing driveway as tandem parking, but no parking is required if the ADU is within one-half mile of public transit or in a designated historic district. An ADU may not be rented for less than 30 days, and separate sale apart from the primary residence is prohibited unless the lot is subdivided.
ADUs built without required building and zoning permits are subject to enforcement under the Zoning Ordinance. Per Section 7703, a zoning violation is a misdemeanor (up to six months in county jail and/or a fine not exceeding $1,000) or, at the prosecutor's discretion, an infraction ($100 first, $200 second, $500 each additional within one year). Each day of violation is a separate offense, and the County may also pursue civil penalties up to $2,500 per day.
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