National City, CA Accessory Structures: Garage Conversions (2026)

National City handles garage conversions through the ADU section of the Land Use Code (Title 18), Section 18.30.380. Subsection F.2 lets an ADU be attached to, located within, or detached from an existing or proposed primary dwelling unit, including garages and habitable or non-habitable accessory structures. Subsection F.3 answers the parking question directly: no additional parking is required for an ADU, and if an ADU is constructed within existing garage or covered parking, no replacement parking spaces can be required. A homeowner who turns a garage into a unit does not have to build a new carport or driveway space to make up for it.

Setbacks follow the structure that is already there. Subsection F.5.c requires no setback for an existing living area or permitted accessory structure, or for a structure built in the same location and to the same dimensions as an existing structure, that is converted to an ADU or to part of one. A new unit or one that is not a same-footprint replacement needs a setback of no more than four feet from the side and rear lot lines. Subsection F.8.d adds that an ADU built within the footprint of an existing dwelling or detached structure has no maximum floor area, and the minimum ADU size is 150 square feet.

On a multi-family lot, subsection D.3 allows multiple ADUs within the portions of existing multi-family structures not used as livable space, and garages are named on that list along with storage rooms, boiler rooms, passageways, attics and basements. Each unit must comply with state building standards for dwellings.

Approval is ministerial under Section 18.12.030, and staff act on the building permit application within 60 days after a complete application is received. For junior ADUs, Section 18.30.390(F)(3) also waives replacement parking when the JADU is created within an existing attached garage, and JADUs are capped at 500 square feet with a separate exterior entry and a kitchen or efficiency kitchen. Separately, Section 18.42.030(B) says no accessory structure can be structurally altered, converted, enlarged or maintained to provide a second dwelling unit unless it is made to conform to all Land Use Code regulations for new structures.