National City Accessory Dwelling Unit Regulations

Introduction to Accessory Dwelling Units

An accessory dwelling unit commonly called a granny flat or in-law suite must exist on a lot that’s zoned single-family. It has its own entrance, separate from the primary house, as well as a kitchen, bathroom and living space. These units can be rented, year-round, and add a lot of value to a property.

Zoning in National City

ADUs are allowed in lots zoned for single-family or multi-family use. A single-family dwelling must already exist on the property or be built simultaneously with the ADU.

ADUs are only allowed on lots with 1 single family residence on the lot.

ADUs are not allowed if the roadways and public utilities or services are determined to be inadequate.

Lot size in National City

There is no minimum or maximum lot size requirement to build an accessory dwelling unit.

Min/Max Building Sizes

Min ADU size is 150 sqft.
The increased floor area of an attached accessory dwelling unit shall not exceed 50 percent of the existing living area, with a maximum increase in floor area of 1,200 square feet.
The total area of floor space for a detached accessory dwelling unit shall not exceed 1,200 square feet.
No max limit for conversions.
Max JADU size is 500 sqft.

Height Restrictions

State Standards don’t specify height restrictions.


Parking requirements do not exceed one parking space per unit or per bedroom.
These spaces may be provided as tandem parking on an existing driveway.

Detached ADU’s are required to have one parking space per bedroom or unit. Off street parking is allowed to be tandem or within the residence’s setbacks given that it is safe to access.Parking not required if the ADU is:

  • Located within ½ mile of public transit
  • Located within an architecturally and historically significant historic district
  • Part of an existing primary residence or an existing accessory structure
  • In an area where on-street parking permits are required, but not offered to the occupant of the ADU
  • Is located within one block of a car share area


Attached ADU’s built within the existing residence do not require additional parking.


No setback shall be required for an existing garage that is converted to an accessory dwelling unit, and a setback of no more than five feet from the side and rear lot lines shall be required for an accessory dwelling unit that is constructed above a garage.

Owner Occupancy

ADU’s cannot be sold separately from the primary residence. The owner is not required to live in the main residence or the ADU.


California passed Senate Bill 1069 in an effort to increase the supply of housing to the state. For this reason, any accessory dwelling unit may be used for a long-term rental.

How to Evaluate ROI

Building an accessory dwelling unit, especially if you intend to keep the property for a few years, represents an enormously beneficial opportunity to maximize your property.

By constructing an accessory dwelling unit you are adding additional square footage to the property. So if you can build a unit for $275 a square foot, but the average value of homes in your neighborhood are worth $400 a square foot you are gaining instant equity through the project. Plus, you also now have the added benefit of a flexible space that can be rented or used for family.

Additional notes

Accessory dwelling units shall not be required to provide fire sprinklers if they are not required for the primary residence and may employ alternative methods for fire protection.

The unit is not intended for sale separate from the primary residence and may be rented.

National City has not passed its own ADU ordinance. (As of January 2019) it is expected that something will be passed in 2019.

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