National City, CA Accessory Structures: ADU Rules (2026)

Section 18.30.380 of the Land Use Code (Title 18) governs accessory dwelling units in National City. A lot qualifies for one ADU when it holds a proposed or existing dwelling, sits in a zone that allows residential use under Table 18.20.020, meets the development standards in subsection F, and is not located where the city manager or designee has determined that public utilities or services are inadequate or that the ADU will hurt traffic flow or public safety. A lot with an existing multi-family building can instead hold two detached ADUs, each capped at 1,200 square feet of floor area and 16 feet in height. Multiple ADUs are also allowed inside the non-livable parts of existing multi-family structures, such as storage rooms, boiler rooms, passageways, attics, basements and garages, and up to 25 percent of the existing number of multi-family dwelling units is allowed.

Approval is ministerial under Section 18.12.030. A staff person designated by the city manager acts on the building permit application within 60 days after a complete application is received. An ADU submitted with a new primary dwelling cannot be approved before the primary dwelling is, and an applicant can request a variance under Section 18.12.120 in the same filing.

Subsection F sets the physical limits. No additional parking is required. On a single-family lot the ADU cannot exceed the height of the primary dwelling or 16 feet, whichever is greater, and the cap rises to 25 feet for an ADU built above a garage or on a lot smaller than 5,000 square feet. The front setback is 15 feet and the side and rear setbacks are 4 feet. The smallest ADU is 150 square feet. An attached unit is capped at 50 percent of the primary dwelling's floor area or 1,200 square feet, whichever is greater, and a detached unit at 1,200 square feet, with no cap for a unit built within an existing footprint. No minimum lot size and no passageway are required, fire sprinklers are required only when the primary residence needs them, and one 24-inch box tree goes in the front setback or the abutting parkway. ADUs must follow the single-family infill standards in Section 18.42.070.C.