Accessory Dwelling Unit Regulations for RS-10 Single-Family Residential District in Concord
Accessory Dwelling Units (ADUs) are permitted by right in the RS-10 Single-Family Residential district as an accessory use to the principal single-family dwelling. Owners must comply with specific size limitations, design standards, and objective criteria to ensure compatibility with the surrounding neighborhood, including requirements for permanent foundations and a prohibition on short-term rentals of less than 30 days.
Permissibility and General Requirements
In the RS-10 Single-Family Residential district, an Accessory Dwelling Unit is a permitted accessory use, subordinate to the principal single-family dwelling [Section 18.30.010, Section 18.200.180]. The RS-10 district is a specific sub-designation within the broader RS Residential Single-Family district, where a minimum lot size of 10,000 square feet is required [Section 18.15.020].
Accessory Dwelling Units in the RS-10 district must adhere to the following general requirements:
- Building Permit: A building permit is required and will be processed ministerially within 60 days of receipt of a complete application [Section 18.200.180].
- Foundation: A permanent foundation is required for all Accessory Dwelling Units [Section 18.200.180].
- Subdivision: An Accessory Dwelling Unit cannot be sold independently of the principal single-family dwelling on the same lot [Section 18.200.180].
- Short-Term Rentals: Rentals of an Accessory Dwelling Unit for terms of less than 30 days are strictly prohibited [Section 18.200.180].
Size and Height Standards
The living area of an Accessory Dwelling Unit in the RS-10 district must be at least 150 square feet. It cannot exceed 50 percent of the floor area of the principal dwelling, subject to specific maximums based on lot size:
| Lot Size Category | Maximum ADU Size |
|---|---|
| Net area < 12,000 sq. ft. | 1,000 sq. ft. (excluding up to 230 sq. ft. for attached garage/carport) |
| Net area ≥ 12,000 sq. ft. | 1,200 sq. ft. (excluding up to 460 sq. ft. for attached garage/carport) |
Note: This size limitation is waived if it restricts the Accessory Dwelling Unit to less than 800 square feet [Section 18.200.180].
Height Limits:
- Attached Accessory Dwelling Units: May not exceed 25 feet in height, or the height of the principal dwelling, whichever is lower [Section 18.200.180].
- Detached Accessory Dwelling Units: Generally limited to 16 feet, though single-story units may exceed this if necessary for architectural compatibility [Section 18.200.180].
Parking Requirements
Parking required for an Accessory Dwelling Unit is in addition to the parking required for the principal single-family dwelling.
| Parking Criteria | Requirement |
|---|---|
| Required Spaces | 1 space per ADU or per bedroom, whichever is less [Section 18.200.180] |
| Parking Location | May be uncovered, tandem, or in the front yard setback (within existing driveway space) [Section 18.200.180] |
Parking Exemptions: Parking is not required for an Accessory Dwelling Unit in the RS-10 district if the unit is:
- Located within one-half mile walking distance of public transit [Section 18.200.180].
- Located within a designated architecturally and historically significant historic district [Section 18.200.180].
- Part of the proposed or existing principal dwelling or a conversion of an accessory structure [Section 18.200.180].
- Located where on-street parking permits are required but not offered to the occupant of the Accessory Dwelling Unit [Section 18.200.180].
- Located within one block of a car share vehicle site [Section 18.200.180].
Design and Setback Standards
Accessory Dwelling Units must provide interior side and rear setbacks of at least four feet. Front and corner-side setbacks must comply with those required for the principal dwelling [Section 18.200.180]. Architectural detailing, such as roof pitch, colors, and materials, should be consistent with the principal dwelling to maintain neighborhood compatibility [Section 18.200.180].
Sections Cited
- Section 18.15.020 (Zoning map and districts)
- Section 18.30.010 (Purpose)
- Section 18.200.180 (Accessory dwelling units)