Accessory Dwelling Unit Size Standards in Concord
In the City of Concord, an Accessory Dwelling Unit (ADU) is generally limited to a maximum size of 1,000 square feet for lots smaller than 12,000 square feet, or 1,200 square feet for lots 12,000 square feet or larger. Regardless of lot size, an ADU must always be at least 150 square feet and cannot exceed 50 percent of the floor area of the principal dwelling, unless such a limit would restrict the ADU to less than 800 square feet, in which case the 800-square-foot limit takes precedence.
Maximum Size Standards for Accessory Dwelling Units
The City of Concord Development Code sets specific size limitations for Accessory Dwelling Units to ensure they remain subordinate to the principal dwelling. The following table outlines the maximum floor area requirements based on lot size:
| Lot Net Area | Maximum Accessory Dwelling Unit Size |
|---|---|
| Less than 12,000 square feet | 1,000 square feet (excludes up to 230 sq. ft. for attached garages/carports) |
| 12,000 square feet or greater | 1,200 square feet (excludes up to 460 sq. ft. for attached garages/carports) |
Key Size Considerations
- Floor Area Ratio (FAR) Limit: In all residential and nonresidential districts, the total building coverage—including the principal structure, any accessory dwelling unit, and all accessory structures—must not exceed the coverage allowed by the applicable district [Section 18.200.030].
- Minimum Size: All Accessory Dwelling Units in the City of Concord must be at least 150 square feet [Section 18.200.180].
- Percentage of Principal Dwelling: An Accessory Dwelling Unit cannot exceed 50 percent of the floor area of the principal dwelling on the lot [Section 18.200.180].
- Exception for Small Units: The 50 percent of floor area limitation is waived if it would restrict the Accessory Dwelling Unit to less than 800 square feet [Section 18.200.180].
- Exempt Accessory Dwelling Units: An "Exempt" accessory dwelling unit, which measures up to 800 square feet and maintains four-foot side and rear yard setbacks, is not subject to lot coverage or floor area ratio standards if those standards would prohibit its construction [Section 18.20.030].
Exclusions and Definitions
For the purpose of calculating the size of an Accessory Dwelling Unit, the "living area" is defined as the interior habitable area of the dwelling unit, including basements and attics, but excludes garages and any habitable accessory structure [Section 18.20.030]. When calculating the maximum square footage allowance, the city excludes specified areas for attached garages or carports as noted in the table above [Section 18.200.180].
Junior Accessory Dwelling Units (JADUs)
It is important to distinguish Accessory Dwelling Units from Junior Accessory Dwelling Units (JADUs). A Junior Accessory Dwelling Unit in the City of Concord is limited to a maximum floor area of 500 square feet and must be contained entirely within the existing walls of a proposed or existing single-family principal dwelling or an attached garage [Section 18.20.030, Section 18.200.180].
Sections Cited
- Section 18.20.030: Definitions
- Section 18.200.030: Accessory structures
- Section 18.200.180: Accessory dwelling units