Accessory Structure Regulations in Concord

Accessory structures at single-family dwellings in Concord must be subordinate to the primary structure and generally cannot exceed 16 feet in height or occupy more than 25 percent of the required rear yard area. Specific size limits for these structures in residential districts are tiered based on the minimum lot size, and they are prohibited from being located in front or street side yards.

General Requirements for Accessory Structures

Accessory structures are defined as buildings or structures that are not part of the principal dwelling on the lot, and their use must be incidental and subordinate to the principal dwelling [Section 18.20.030].

Relationship to Primary Structure: Accessory structures must be incidental and subordinate to the primary use or character of the site [Section 18.200.030].
Timing of Construction: Accessory structures must be constructed concurrently with or subsequent to the construction of the primary structure on the property [Section 18.200.030].
Prohibited Locations: Accessory structures are prohibited in front and street side yards and may not project beyond the front building line of the primary structure [Section 18.200.030].
Design Standards: Accessory structures must be subordinate to the primary structure in size, height, location, and appearance. Roofing, siding, and color schemes must be consistent with or complementary to the primary structure [Section 18.200.030].
Separation: A minimum five-foot separation must be maintained between all structures on the lot, including the primary structure, except that carports and patio covers may be located immediately adjacent to the primary structure [Section 18.200.030].

Size Limits in Residential Districts

The maximum floor area for accessory structures located in rear yards is determined by the minimum lot size of the property in residential districts [Section 18.200.030].

Table 1: Maximum Floor Area for Accessory Structures

Minimum Lot Size (Square Feet)	Maximum Floor Area for Accessory Structures in Rear Yards (Square Feet)
Less than 5,000	To be specified in the subdivision or use permit approval
6,000	480
8,000	560
10,000	800
12,000	800
15,000	800
20,000	1,000
40,000	2,000

Note: An increase of up to 10 percent in floor area may be allowed subject to a minor exception approval [Section 18.200.030].

Setbacks and Height Standards

Accessory structures must comply with specific height and setback limitations [Section 18.200.030]:

Standard Height Limit: Accessory structures that meet the primary structure setback requirements shall not exceed 16 feet in height.
Reduced Setback Heights: Accessory structures between 6 and 12 feet in height must maintain a minimum five-foot side and rear setback. The height may be increased by one foot for every two feet of additional setback provided, up to a maximum height of 16 feet.

Exemptions

The following structures are exempt from these specific accessory structure regulations [Section 18.200.030]:

Structures less than 120 square feet in area.
Structures six feet or less in height.
Structures that do not require a building, electrical, or mechanical permit.
Structures that are not placed on a permanent foundation.

Additionally, certain decks, patios, and terraces under 30 inches in height are permitted closer to property lines as specified in Section 18.200.030. Accessory dwelling units (ADUs) are not considered "accessory structures" for these regulations and are subject to separate requirements under Section 18.200.180.

Sections Cited