What you can build

National City ADU Regulations & Zoning


Size and Separation

Maximum size 1200 square feet

Side/rear setbacks 4 feet

Two story Yes

Building separation 5 feet

Additional Requirements

Soils Report Yes

Building Verification Survey No

Coastal permit (in some areas) Yes

Stormwater Mitigation No

Number of ADUs Allowed

How many ADUs can you build in National City?

On National City single-family residential lots, you may build one ADU (either attached or detached) and one Junior ADU (JADUs have an owner occupancy requirement and must be converted from existing space within the primary residence).

How many ADUs does National City allow for multifamily properties?

National City allows up to 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)

Non‐livable space within existing multi‐family structures may be converted into an ADU. Examples of areas that can be converted include storage rooms and garage spaces. The maximum number of ADU allowed in a multi‐family structure is equal to 25% of the number of existing multi‐family units in the structure. Fractional units are rounded down. A minimum of one conversion ADU is allowed.

ADU Size & Building Constraints

What size detached ADU can you build in National City?

National City allows for up to a 1200 sqft detached ADU. An ADU constructed within the footprint of an existing dwelling or a detached structure shall not be subject to a maximum square footage of total floor area (so you could convert a large barn, for example, of any size).

What is the height requirement for an ADU in National City? Can you build a two story ADU?

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 and height limits.

How big can an attached ADU be in National City?

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.

What are the design requirements for ADUs in National City?

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.


What is the setback requirement for an ADU in National City?

For all ADUs, the front setback shall be a minimum of 15 feet, the exterior and interior side yard setback shall be a minimum of 4 feet, and the rear yard setback shall be a minimum of 4 feet.

No setback shall be required for an existing living area or permitted accessory structure or a structure constructed in the same location and to the same dimensions as an existing structure that is converted to an accessory dwelling unit or to a portion of an accessory dwelling unit.

What is the minimum distance the ADU must be from existing structures?

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

Additional Requirements

Does National City require in-person submission of plans for an ADU?

No, National City allows digital submission of applications for an ADU.

Does National City require a soils report for an ADU?

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

Does National City require coastal development permits?

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.


How many ADUs does National City allow for multifamily properties?

Two detached ADUs are permitted on lots with an existing multi-family residential dwelling. Note that the building itself is what will qualify, not just the underlying zoning — so you could likely just build one ADUs on a multifamily zoned property that currently has a single family home on it.

Additionally, you can convert existing non-livable space within an ADU up to 25% of the existing dwelling units.

Can you stack detached ADUs on top of each other?

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

Can you attach two ADUs to each other in National City?

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.

Can you convert existing space to an ADU?

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.


What is the parking requirement for an ADU in National City?

No additional parking is required for an ADU. If an ADU is constructed within existing garage or covered parking, then no replacement parking spaces may be required.

Where can a parking space be located?

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.

Additional National City ADU Regulation Resources

National City Municipal Code – 18.30.380 Accessory Dwelling Units