National City ADU Regulations & Zoning

National City allows at least 2 detached ADUs for multifamily lots with an existing multi-family building. (Meaning: In order to build 2 ADUs, the property must already have at least a duplex on it, not just a single family dwelling)

Multifamily property owners are permitted to build as many ADUs as there are existing units, with a maximum of eight detached ADUs.

Additionally, a minimum of one accessory dwelling unit, or up to 25 percent of the existing multifamily units, is permitted within an existing multifamily dwelling, as a result of the conversion of non-habitable space including, but not limited to, storage rooms, boiler rooms, passageways, attics, basements, or garages.

Read more about the rules around how many ADUs you can build on a multifamily lot.

Per the National City ADU code, attached or detached ADUs shall not exceed the height of the primary dwelling or 16 feet, whichever is greater. For an ADU constructed above a garage or on a lot smaller than 5,000 square feet, the height shall not exceed 25 feet. On a property with a multi-family residential structure, the height of a detached ADU shall not exceed 16 feet.

Also, per recent state law change, detached ADUs within half a mile of major transit stops or high-quality transit corridors can use 4′ side & rear setbacks, up to 18 feet tall. An additional 2 feet can be added if the ADU’s roof pitch matches the primary dwelling. This 18’+2′ limit would allow for a two story unit.

Read more about two story ADUs & height limits and building an ADU above a garage.

The square footage of any attached ADU may not to exceed 50% of the primary dwelling square footage, or 1,200 sqft, whichever is less, but not less than 800 square feet.

All ADUs are required to be compatible with the primary unit. This typically means compatible in terms of design, building and roofing materials, colors, and exterior finishes.

One twenty-four-inch box tree shall be planted within the required fifteen foot front yard setback for ADUs or in the abutting parkway. Existing trees that are at least fifteen feet high and fifteen feet in width may be used to satisfy this requirement.

The minimum required distance between structures is 5 feet in National City.

Yes, National City requires a soils report for ADUs of 500sqft or more.

Yes, accessory dwelling units developed within the coastal zone may be subject to the permit requirements of the Local Coastal Program. We will investigate if you are eligible for a waiver, which is possible in some cases. Read more about ADUs in the coastal zone.

No, because an ADU cannot stand higher than 16′ on multifamily properties.

Yes, if the lot has an existing multi-family residential structure you can propose to construct up to two detached ADUs in an attached configuration as long as it meets all underlying zoning, life safety, and building code requirements.

Yes, existing non-livable space may be converted to ADUs (e.g. storage areas and garages). There is no limit on the number of ADUs that can be created in this manner. These conversions are in addition to the allowed number of detached ADUs.

All information verified with a planner for National City in November 2022.

If a parking space is required, it may be located within the setbacks and in an existing driveway as tandem parking. Parking spaces don’t need to be replaced when a garage, carport, or covered parking structure is demolished in conjunction with the construction of an ADU or converted to an ADU.