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What you can build
National City ADU Regulations & Zoning
KEY RULES AT A GLANCE
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
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).
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)
Effective Jan 2025 (SB1211): Multifamily property owners are permitted to build as many ADUs as there are existing units, with a maximum of eight detached ADUs. This change is due to California state law and will pre-empt existing local laws that are not brought into conformance.
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
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).
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.
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.
Setbacks
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.
The minimum required distance between structures is 5 feet in National City.
Additional Requirements
No, National City allows digital submission of applications for an ADU.
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.
Parking
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.
Effective Jan 2025 (SB1211): When a garage, carport, covered parking structure, or uncovered parking space is demolished or converted for construction of an ADU, replacement parking will not be required.
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.