Concord | ADUs and SB 9

Concord, California ADUs and SB 9: ADU Sizes, Heights and Setbacks, Junior ADUs, Pre-Approved Plans, Fees and SB 9 Two-Unit Projects

An accessory dwelling unit (ADU) is a second home on a lot that already has, or will have, a main home. A junior ADU (JADU) is a unit of 500 square feet or less inside a house. Concord's ADU rules are one long section of the Development Code, 18.200.180, last amended by Ordinance 23-8 on October 3, 2023. State ADU law has changed several times since then, and parts of the City section are now stricter than the state statutes allow. This page sets out the City section, the places where state law controls, the pre-approved plans, the fees, and how the City handles SB 9 two-unit projects. The Concord overview has the summary.

ADU Types and Limits

Source: Concord Development Code, Section 18.200.180, subsections (B), (C)(8), (C)(16), (C)(17) and (D), as amended by Ordinance 23-8 of October 3, 2023.

The section's purpose line says it exists "to comply with California Government Code Sections 65852.2 and 65852.22." The Legislature moved the ADU statutes in 2024, and they are now at Government Code 66310 to 66342. The section ends with a rule for that situation: if the Legislature amends state law "so as to give rise to a conflict between state law and any provision or provisions of this section, such amendment shall prevail and apply in place of the conflicting provision." The state rules are on the California ADU law page.

Where an ADU Is Allowed and How Many

• Districts. Subsection (C)(7) lists the districts: R (Residential), NTS (North Todos Santos), CO (Community Office), CMX (Commercial Mixed-Use), NC (Neighborhood Commercial), DP (Downtown Pedestrian) and DMX (Downtown Mixed-Use). Subsection (D) adds lots "with a lawfully constructed single-family or multifamily principal dwelling in other zoning districts."
• One ADU under the standards. "One accessory dwelling unit that complies with the development and design standards in subsection (C) of this section shall be permitted on a lot with an existing or proposed single-family or multifamily principal dwelling."
• Or the exempt units. Where no such ADU exists or is proposed, the City must approve "One interior accessory dwelling unit and one junior accessory dwelling unit per lot," or "One detached, new construction accessory dwelling unit and one junior accessory dwelling unit" where the detached unit "does not exceed 800 square feet in floor area."
• Apartment lots. "Up to two detached accessory dwelling units on a lot with a proposed or existing multifamily principal dwelling," and conversions of non-livable space "equivalent to up to 25 percent of the number of existing, legally permitted units in the multifamily principal dwelling, or one, whichever is greater."
• Density. An ADU or junior ADU "shall not be considered to exceed the allowable density for the lot upon which it is located."
• No separate sale. An ADU "may not be sold independently of the single-family principal dwelling or multifamily principal dwelling but may be leased separately." The section allows one exception, for homes built by a qualified nonprofit and sold as tenants in common.
• Rental term. "The accessory dwelling unit or junior accessory dwelling unit shall not be rented for a term of less than 30 days."

Size, Height and Setbacks

• Size. "The living area of an accessory dwelling unit shall be at least 150 square feet in size, and shall not exceed the lesser of 50 percent of the floor area of the principal dwelling or" 1,000 square feet "on lots with a net area of less than 12,000 square feet," or 1,200 square feet on larger lots. The 1,000 foot figure leaves out "up to 230 total square feet for attached garages or carports," and the 1,200 foot figure leaves out 460.
• The 800 foot minimum. "This limitation will be waived if it limits the size of the accessory dwelling unit to less than 800 square feet." Subsection (C)(18) repeats the point for coverage, floor area ratio, front setback and open space, which "must permit or shall be waived to allow a detached or attached accessory dwelling unit up to 800 square feet in size with four-foot side and rear yards."
• Living area. The section counts "the interior habitable area of a dwelling unit, including basements and attics but not garages."
• Detached height. "Sixteen feet on a lot with an existing or proposed single-family principal dwelling or multifamily principal dwelling." A one-story ADU may go higher "when the planning division determines additional height is necessary to provide greater compatibility with the roofline, pitch or architectural style of the principal dwelling."
• Near transit. Eighteen feet "if the lot is within one-half mile walking distance of a major transit stop or a high-quality transit corridor, as those terms are defined in Public Resources Code Section 21155," with "An additional two feet in height" for a matching roof pitch. The City's ADU Regulations page puts it as "within one-half mile of a BART station or Clayton Road."
• Attached height. "The height of an attached accessory dwelling unit shall not exceed 25 feet or the height limitation that applies to the single-family principal dwelling or multifamily principal dwelling, whichever is lower. However, the accessory dwelling unit may not exceed two stories."
• Above a garage. An ADU on the second story of an accessory structure "may exceed 16 feet in height, provided they maintain interior and corner side setbacks of at least 10 feet and meet the height and rear setback standards applicable to the principal dwelling."
• Setbacks. "Accessory dwelling units shall provide interior side and rear setbacks of at least four feet." In front, "In cases where the principal dwelling encroaches into the setback, the accessory dwelling unit may encroach to the same extent as the principal dwelling."
• Hillside and creek lots. "The living areas of accessory dwelling units proposed on any hillside lot are exempt from the hillside development use permit requirements." Garages or sheds built with the ADU are not exempt. An ADU near a creek must meet the creek setback standards but is "exempt from the design and site review application requirement."

Design and Parking

• Matching the house. Colors and materials must be consistent with the main home "using at least two of the following three approaches": one matching exterior color, two matching exterior materials, or "A matching roof slope to that of the dominant roof pitch or form of the principal dwelling." Pre-approved City plans are released from this standard.
• Entry. An attached ADU needs "a separate exterior entrance from the single-family principal dwelling that is not located on the same side or facing in the same direction as the entrance for the principal dwelling."
• Upper windows. "Avoid direct line of sight to existing neighboring units by staggering window and door placement."
• Porches. A porch for an exempt ADU in a front or corner side setback may be "no more than five percent of the size of the livable area of the exempt ADU up to 40 square feet."
• Exempt units. ADUs that meet subsection (D)(2) "do not have to meet the additional development and design standards in the underlying zoning district or in this section to be permitted."
• Parking. "one off-street parking space is required per accessory dwelling unit or per bedroom, whichever is less." Spaces "may be uncovered, tandem, and/or located in the front yard setback if contained within the space of an existing or proposed driveway."
• Wider driveway. A driveway may be widened for the space if no more than 50 percent of the required front setback or yard area ends up paved, and no new curb cut is added unless the driveway rules allow it.
• Five exemptions. No parking is required where the ADU "is located within one-half mile walking distance of public transit," is in a designated historic district, "is part of the proposed or existing principal dwelling or conversion of an accessory structure," where street parking permits are required and not offered to the occupant, or where a car share vehicle site is within one block.
• Public transit. The section defines it as "a location where the public may access buses, trains, subways, and other forms of transportation that charge set fares, run on fixed routes, including, but not limited to, a bus stop or train station."
• Lost garage. "When a garage, carport, or covered parking structure is demolished in conjunction with the construction of an accessory dwelling unit or converted to an accessory dwelling unit, the demolished parking is not required to be replaced."

Junior ADUs

• Where. "One junior accessory dwelling unit is allowed on lots zoned to allow single-family principal dwellings and is not permitted on a property with a multifamily principal dwelling."
• Inside the house. A junior ADU "must be constructed entirely within the walls of an existing or proposed single-family principal dwelling or an attached garage," and has "a maximum floor area of 500 square feet."
• Entrance. It "shall have a separate exterior entrance from the proposed or existing single-family principal dwelling unit."
• Bathroom. "Access to a bathroom is required, which may be part of the junior accessory dwelling unit or located in the existing or proposed single-family principal dwelling." Where the bathroom is in the house, the junior ADU "shall have internal access."
• Kitchen. An efficiency kitchen "includes a cooking facility with appliances, a food preparation counter, and storage cabinets."
• Parking. "No additional parking is required for junior accessory dwelling units."
• Covenant. Before the certificate of occupancy, the owner records a covenant that prohibits separate sale, restricts the size, prohibits "renting the property for fewer than 30 consecutive calendar days," and requires an owner to live on site. State law now narrows that last term, as explained below.

The Permit and the Pre-Approved Plans

• One permit. "The building permit application shall be ministerially processed within 60 days of receipt of a complete application and shall be approved if the proposed unit conforms to the requirements of this section." Ministerial means staff check the application against fixed rules, with no hearing.
• With a new house. An ADU filed with a new main home is not acted on until the main home is decided, and "Occupancy of the junior accessory dwelling unit or accessory dwelling unit shall not be allowed until the city approves occupancy of the single-family principal dwelling."
• Existing problems. "The city will not deny a building permit application for an accessory dwelling unit because of nonconforming zoning conditions, building code violations, or unpermitted structures on the property that do not present a threat to public health and safety and are not affected by the construction of the accessory dwelling unit."
• Foundation. "A permanent foundation system" is required for all ADUs.
• Custom plans. The City's custom ADU process page lists four steps: meet with a planner, hire a designer, compile the forms in the submittal requirements, and apply for a building permit. "Typical plan check review times and fees will apply."
• Pre-approved plans. With a City plan, "the only plan review that is required is for your site specific site plan," and "this review only takes 5 business days." The design "cannot be revised and must be permitted as designed," although the ADU "may be oriented in any direction and floor plans may be mirrored."
• Other options. The City also lists pre-approved plans from private designers, where "The applicant must also work directly with the designer to pay for use of the plans," and pre-fabricated ADUs whose plans a state or federal agency has approved.

Source: City of Concord, pre-approved ADU plans page, read October 10, 2026.

ADU Fees and the Rebate

Source: City of Concord, Fees and Charges for Various Municipal Services, Resolution No. 26-6042.1, Section D, items 28, 31, 37 and 48. The schedule prints no heading above rows 28.1 to 28.6; their amounts are in the column headed "Tran."

• The 750 foot line. Government Code 66311.5 says a city "shall not impose any impact fee upon the development of an accessory dwelling unit that has 750 square feet of interior livable space or less," and that fees on a larger ADU "shall be charged proportionately in relation to the square footage of the primary dwelling unit." The schedule's rows start at 750 square feet, so ask how the City treats an ADU of exactly 750. An impact fee is a charge on new building that pays for public facilities.
• Sewer. The same statute says an ADU created inside an existing house under its first category may not be charged "a related connection fee or capacity charge, unless the unit was constructed with a new single-family dwelling."
• What the City tells owners. The ADU FAQ handout says "You are required to pay plan check and permit fees to the building division, which are often a few thousand dollars." That is the City's own description, with no fixed figure.
• Rebate. The ADU Rebate Program page offers "rebates of up to $15,000": $7,500 for an ADU of 500 square feet or less, $5,000 for 501 to 750 and $2,500 for 750 to 1,000, and double those amounts where the owner records a 20-year low-income deed restriction. The page says "Applications must be submitted prior to September 30, 2026." That date had passed when the page was read on October 10, 2026, so ask the City whether the program is still open.

Where the City Section and State Law Differ

A city ADU rule that is stricter than the state statutes has no effect to that extent, and the Concord section itself says later state amendments prevail. The differences found on October 10, 2026:

• Owner occupancy for an ADU. Subsection (C)(15) requires it "for building permit applications received after December 31, 2024." Government Code 66315 says "No additional standards, other than those provided in Section 66314, shall be used or imposed, including an owner-occupant requirement." The City FAQ agrees with the statute: "An ADU does not have an occupancy requirement."
• Owner occupancy for a junior ADU. The City covenant requires an owner on site for every junior ADU. Government Code 66333, amended effective January 1, 2026, says "Owner-occupancy shall not be required if the junior accessory dwelling unit has separate sanitation facilities."
• How many units on a house lot. The City section allows either one ADU under its standards or a set of exempt units. Government Code 66323 requires approval of the listed units "or any combination of the following units": an ADU and a junior ADU within the house or an accessory structure, and "One detached, new construction, accessory dwelling unit."
• Detached ADUs on apartment lots. The City section says up to two. The statute says "On a lot with an existing multifamily dwelling, not more than eight detached accessory dwelling units," as long as the number does "not exceed the number of existing units on the lot," and two on a lot with a proposed building.
• The 50 percent cap. The City sentence applies the 50 percent cap to every ADU. Government Code 66314 applies it to "an attached accessory dwelling unit" and sets a separate limit: "The total floor area for a detached accessory dwelling unit shall not exceed 1,200 square feet." The City FAQ handout also limits the 50 percent rule to an attached ADU.
• The minimum size. The City waives its cap below 800 square feet. Government Code 66321 prohibits a maximum size under "Eight hundred fifty square feet of interior livable space," or "One thousand square feet of interior livable space for an accessory dwelling unit that provides more than one bedroom."
• Design review. The City section says that where a design misses two of its three matching approaches, "a discretionary design and site review process is required." Government Code 66317 says an ADU permit "shall be considered and approved ministerially without discretionary review or a hearing."
• Appeals. The City section says "No appeals are permitted." The statute now says that after a denial or a finding that an application is incomplete, the agency "shall provide a process for the applicant to appeal that decision in writing to the governing body of the agency."
• A sixth parking exemption. Government Code 66322 also prohibits parking standards "When a permit application for an accessory dwelling unit is submitted with a permit application to create a new single-family dwelling or a new multifamily dwelling on the same lot." The City list has five exemptions.
• Uncovered parking. The statute prohibits a replacement rule when "uncovered parking space is demolished" for an ADU. The City sentence names garages, carports and covered parking structures.

Three smaller points are inside the City's own documents. The section defines an efficiency unit as "a dwelling unit with a maximum floor area of 150 square feet," while its size rule treats 150 square feet as the minimum. Subsection (D)(2) sends the reader to "the allowed height in subsection (C)(18)," but height is in (C)(17). And the City's ADU Regulations page cites "Section 18.200.180(E)(6)" for height exceptions, while subsection (E) of the code is the junior ADU subsection.

SB 9 Two-Unit Projects

SB 9 is the 2021 state law that makes a city approve two primary homes on a lot in a single-family zone with no hearing. Government Code 65852.21 says such a project "shall be considered ministerially, without discretionary review or a hearing." Concord's code has no SB 9 chapter. Its one mention is in Section 18.415.030, which exempts from design and site review "Residential development eligible for ministerial approval under the California HOME Act (SB 9), Government Code Sections 65852.21 and 66411.7." The working rules are in the City's SB 9 handout, last updated 4/28/26.

Source: City of Concord, SB 9 Application and Informational Handout, last updated 4/28/26.

• Who cannot use it. The handout lists sites that are not eligible, among them a site that "Contains wetlands, special flood hazard areas, or regulated floodways," one "Located in a delineated earthquake fault zone," and one that "Contains a designated historic resource."
• Existing tenants. A project is not eligible if it requires demolition or alteration of deed-restricted affordable rental housing, "rent-controlled housing, or housing occupied by a tenant in the last three years." The checklist points to the City's rent stabilization rules for what counts as rent-controlled.
• Standards. "If any requirement would physically preclude an SB 9 unit from being at least 800 square feet in floor area, the requirement may be reduced or waived as determined necessary by City staff."
• Driveways. "Only one driveway is allowed per parcel, except for limited circumstances." The handout adds that "Minimum driveway widths start at 12 feet" and "The minimum driveway length is 20 feet."
• Density bonus. "State Density Bonus Law is not applicable to SB 9 projects."
• Check first. An optional SB 9 Eligibility Determination "typically takes 4-6 weeks" and uses a $2,000 deposit. The letter "does not constitute a formal approval."
• Apply. For a project with no lot split, "Apply for a building permit for a new residential unit or units through the Building Division," which the handout puts at two to three months.

Three points in the handout need a question to the City. Its parking line names only BART and car share, while a footnote in its own checklist says that, as of February 2024, bus stops along Clayton Road qualify as a high-quality transit corridor, which the statute also treats as a reason to waive parking. The checklist asks for an owner occupancy affidavit on "all SB 9 projects," and the two-unit statute contains no affidavit. And the Housing Element's Objective 9.3 promises an ordinance "allowing ADUs and JADUs to be constructed in addition to the two conventional dwelling units per lot provided for by SB 9" by July 2026. The code's Ordinance List through September 8, 2026 shows no such ordinance. Lot splits are on the lot size and subdivisions page.

Limits of This Page

The code text is the publisher's copy, current through Ordinance 26-2 of September 8, 2026, and its Ordinance List shows no ADU ordinance after Ordinance 23-8 of October 3, 2023. The City's agenda system did not answer on October 10, 2026, so this page cannot say whether an ADU or SB 9 ordinance is before the Planning Commission or City Council. The junior ADU covenant form, the SB 9 deed restriction and affidavit forms, the building permit fee tables, the drawings of the six City plans and the map of high-quality transit corridors were not read. School fees and water district charges belong to outside agencies and are not given. Ask the Planning Division at (925) 671-3152 which rules it applies where this page shows a difference from state law.

Where to Go Next

Related on VanPlex: the Concord overview, the California ADU law page and the California SB 9 page.

Frequently Asked Questions

Official sources (checked October 2026)