ADU rules in Concord

Concord allows ADUs wherever a single-family or multifamily home exists or is proposed: CMC 18.200.180(C)(7) lists the R (Residential: RR, RS, RL, RM, RH), NTS, CO, CMX, NC, DP and DMX districts, and subsection (D) extends ADUs to lots in any other district that hold a lawfully constructed home. Locally a lot gets one local-standards ADU under (D)(1) or, only where none exists or is proposed, state-exempt units under (D)(2): one detached new-construction ADU of up to 800 sq ft with 4-ft side and rear setbacks plus a JADU on a single-family lot, or up to two detached ADUs beside a multifamily building. State law widens those counts: Gov. Code 66323(a), as amended by SB 543, requires ministerial approval of 'any combination' of a converted ADU, a detached 800 sq ft ADU and a JADU on a single-family lot and of up to eight detached ADUs (never more than the existing unit count) beside an existing multifamily building, and HCD's March 2026 handbook says at least one 66314 local-standards unit must be allowed in addition. Detached units go through a ministerial building permit with no hearing.

Attached ADUs (sharing at least part of a wall with the home), interior conversions of existing or proposed living space or an attached garage, and conversions of existing accessory structures are allowed in the same districts (18.200.180(B), (C)(7), (D)). An attached ADU may reach 25 ft or the home's height limit, whichever is lower, but no more than two stories (C)(17)(a), and needs its own entrance that is not on the same side or facing the same direction as the home's entrance unless screened from street view (C)(10)(b). A conversion within an existing home or accessory structure qualifies as a state-exempt unit under (D)(2)(a), with up to 150 sq ft of expansion for ingress and egress, and a JADU of up to 500 sq ft may be built within a single-family home or its attached garage, one per single-family lot and none on a multifamily property (E)(1). On multifamily lots, ADUs converted from non-livable space (storage rooms, attics, basements, garages) are allowed up to 25 percent of the existing units, or one, whichever is greater (D)(2)(d).

CMC 18.200.180(C)(8) caps a local-standards ADU at the lesser of 50 percent of the principal dwelling's floor area or 1,000 sq ft on lots with a net area under 12,000 sq ft (an attached garage or carport of up to 230 sq ft not counted) or 1,200 sq ft on lots of 12,000 sq ft or more (up to 460 sq ft excluded), with a 150 sq ft minimum, and waives the limit 'if it limits the size of the accessory dwelling unit to less than 800 square feet'. Size is measured as living area, 'the interior habitable area of a dwelling unit, including basements and attics but not garages', which tracks Gov. Code 66313(f); both caps sit at or above the 850 and 1,000 sq ft floors of 66321(b)(2), and the 800 sq ft waiver supplies the allowance 66321(b)(3) requires of percentage limits. A state-exempt detached unit is limited to 800 sq ft (D)(2)(b), a JADU to 500 sq ft, and a conversion to the existing space plus 150 sq ft. Heights follow 66321(b)(4): 16 ft detached, 18 ft within one-half mile walking distance of a major transit stop or high-quality transit corridor plus 2 ft to match the home's roof pitch, 18 ft beside a multistory multifamily building, no limit for a converted detached accessory structure, and 25 ft or the home's limit for attached units, at most two stories (C)(17).

No owner occupancy for ADUs, by state preemption over the codified text. CMC 18.200.180(C)(15)(a), adopted 10-3-2023, still requires one dwelling to be an owner's principal residence for 'building permit applications received after December 31, 2024'; Gov. Code 66315 bars 'an owner-occupant requirement' on ADUs with no sunset (the 2023 change HCD's 5-11-2026 letter lists), and the section's own savings clause (H) makes a conflicting state amendment 'prevail and apply in place of' the local provision. The city's ADU FAQ says 'An ADU does not have an occupancy requirement', and its forms list carries an owner-occupancy agreement only for JADUs. For JADUs, (C)(15)(b), (E)(4)(d), the city hub and the 'JADU Occupancy Agreement' deed restriction still require the owner to live in the home or the JADU in every case, but since 1-1-2026 Gov. Code 66333(b), as amended by AB 1154, allows that only where the JADU shares sanitation with the main home, so a JADU with its own bathroom carries no owner-occupancy duty.

CMC 18.200.180(C)(11)(a) requires 'one off-street parking space ... per accessory dwelling unit or per bedroom, whichever is less', which may be uncovered, tandem or in the front setback on a driveway, and (C)(11)(b) waives it within one-half mile walking distance of public transit (defined to include any bus stop or train station), in a council-designated historic district or landmark, for an ADU within the existing or proposed home or a converted accessory structure, where on-street permits are required but not offered, and within one block of a car-share vehicle. Gov. Code 66322(a)(6) adds a waiver the local list omits, for an ADU applied for together with a new single-family or multifamily dwelling, and HCD's March 2026 handbook says no parking may be imposed on 66323 state-exempt units and that a studio adds no bedroom, so on the code's own 'whichever is less' wording a studio needs no space, although the city's July 2023 FAQ and Regulations page say one space for a new ADU. No replacement parking is owed when a garage, carport or covered space is converted or demolished (C)(11)(c), and 66314(d)(11) extends that to uncovered spaces. JADUs need no parking (E)(3).

ADUs and JADUs need only a building permit, which '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' (18.200.180(C)(1)); they are exempt from Design and Site Review (C)(10)(e) and 18.415.030(J), from the hillside development use permit for the living area (C)(12), and from design review in creek and riparian areas (C)(13). The city's permit page says ADUs 'do not require a public review process' and are approved by staff, its 2025 Housing Element progress report lists all 82 ADU applications filed in 2025 as ministerial (Table A), and complete applications using the free pre-approved plans may be permitted within five working days. Two codified clauses yield to Gov. Code 66317 as amended by SB 543: (F) says 'No appeals are permitted', while 66317(d)(1) has required since 1-1-2026 an appeal of an incompleteness finding or a denial to the Council or Planning Commission, and 66317(a)(2) adds a 15-business-day completeness notice. A design meeting fewer than two of the three color, material and roof-pitch matching tests in (C)(10)(a) is routed to discretionary Design and Site Review, a fallback in tension with the ministerial-only rule of 66316 and 66317(a)(1).

CMC 18.200.180(C)(5) says an ADU or JADU 'shall not be rented for a term of less than 30 days', and (C)(4)(a) lets either be leased separately but never sold apart from the main home; the qualified-nonprofit tenancy-in-common exception in (C)(4)(b) cites legacy 65852.26 (now Gov. Code 66341), and there is no Gov. Code 66342 condominium opt-in. The 30-day floor matches Gov. Code 66315 for ordinary ADUs, but 66333(g) and 66323(e) require terms longer than 30 days for JADUs and state-exempt units, one day past the local text and the JADU covenant's 'fewer than 30 consecutive calendar days' ((E)(4)(c)). Concord has no short-term rental permit chapter, so the ADU clause is the operative bar, and stays of 30 days or less count as transient occupancy for the 10 percent hotel tax (3.15.220, 3.15.230). Permitted ADUs and JADUs are fully exempt from the Residential Tenant Protection Program's rent stabilization, just-cause and annual rent registry rules (19.40.020(1)(h)), while a parcel with four or more rental units falls under the Chapter 15.50 multifamily rental inspection program.