ADU Pass
Contra Costa County
ADU Pass helps homeowners in Contra Costa County, California navigate the permit paperwork for building an accessory dwelling unit. We cover 32 cities and 58 ZIP codes in this county.
Map
County ADU details
County ADU ordinance
Contra Costa County (1.16M residents in the East Bay) administers a county ADU ordinance for unincorporated territory under California Government Code Sec. 65852.2 and 65852.22 (the state ADU and JADU statutes). The county code permits attached, detached, and converted ADUs and Junior ADUs in single-family and multi-family residential zoning districts in the unincorporated areas. The ordinance must comply with the strong statewide ADU preemption framework: ministerial review, 60-day permit clock, 800-1,200 sqft minimum allowed sizes, no owner-occupancy through 2025 (returning per AB 976 thereafter), reduced parking requirements, no setback requirements for converted-space ADUs, and SB 13 fee waivers for ADUs under 750 sqft.
Code citations:
- Contra Costa County Code Title 8 Zoning, Chapter 82-24 - Accessory Dwelling Units
- California Government Code Sections 65852.2 / 65852.22
State-floor overlay: California ADU preemption is the strongest in the United States. AB 2221, AB 1033, SB 1211, SB 9 (lot splits), and the long-running annual amendments to Sec. 65852.2 establish a comprehensive state floor that local jurisdictions cannot weaken.
Adopting body: Contra Costa County Board of Supervisors
County permitting (unincorporated parcels)
Contra Costa County Department of Conservation and Development (DCD) issues ADU permits for parcels in unincorporated Contra Costa. Major unincorporated communities include Alamo, Diablo, Discovery Bay, El Sobrante, Kensington, North Richmond, Pacheco, Rodeo, San Ramon (portions), Tara Hills, and others. Incorporated cities (Antioch, Brentwood, Clayton, Concord, Danville, El Cerrito, Hercules, Lafayette, Martinez, Moraga, Oakley, Orinda, Pinole, Pittsburg, Pleasant Hill, Richmond, San Pablo, San Ramon, Walnut Creek) handle their own ADU permits. Pre-application confirmation of jurisdiction is the critical first step for any parcel near a city boundary.
Process overview: Ministerial 60-day review under Cal. Gov't Code Sec. 65852.2: (1) ADU application and site plan; (2) zoning conformance check; (3) building-code plan review against 2022 California Building Code (CBC) including CalGreen Tier 1 and 2022 California Energy Code; (4) septic / sanitary review where applicable (large portions of unincorporated Contra Costa are on Central Sanitary or Delta Diablo sewer; the eastern portion has on-site septic); (5) fire-protection review with the Contra Costa County Fire Protection District or East Contra Costa Fire Protection District (eastern portion); (6) issuance, construction, inspections, certificate of occupancy.
Impact fees: SB 13 (Cal. Gov't Code Sec. 65852.2(f)(3)) waives all impact fees for ADUs under 750 sqft. ADUs 750-1,200 sqft pay impact fees proportionate to size relative to the primary dwelling.
County assessor
The Contra Costa County property assessor / equalization office maintains parcel-level assessment records for all real property in Contra Costa County. ADU additions are typically captured as improvements to the host parcel via shared permit data with the building department. California property-assessment rules govern annual revaluation cycles, homestead or principal-residence caps where applicable, and the procedures for protesting an appraisal.
Assessment policy: Improvement value for an ADU is added to the parcel record on the next regular revaluation cycle. Homestead / principal-residence caps where applicable shield the existing structure from rapid valuation increases but do not exempt new improvement value.
County overlays (3)
Contra Costa County administers flood-hazard, and (where mapped) coastal, wildland-fire, historic, and airport overlays that shape ADU project feasibility. The most consistent overlay across the county is FEMA NFIP floodplain regulation; other overlays apply to specific geographies inside the county.
- FEMA NFIP Special Flood Hazard Areas in Contra Costa County — A new ADU in a mapped SFHA must be elevated to or above the Base Flood Elevation; cost impact on the project is often material.
- Wildland-Urban Interface (WUI) hazard areas
- Historic districts and individually-listed historic resources
California state — ADU law and programs
State ADU law
California has the most aggressive statewide ADU preemption regime in the US, built from ~15 bills passed 2019-2025 and enforced by the Department of Housing and Community Development (HCD). The 2026 HCD ADU Handbook addendum (in effect with the 2025 Title 24 code cycle) is the operative state-level reference. The regime does four things at once: (1) preempts local zoning that would ban or unreasonably restrict ADUs; (2) imposes by-right ministerial approval with short statutory deadlines; (3) caps fees and utility-connection charges; and (4) empowers HCD to void non-compliant local ordinances.
State HOA preemption
California has the strongest statewide HOA-preemption regime in the US for accessory dwelling units, built from two bills: AB 670 (2019) voided ADU-prohibiting covenants on single-family residential lots, and AB 3182 (2020) extended and codified the preemption into the Davis-Stirling Common Interest Development Act (Civil Code §§ 4740 / 4741). The combination prohibits common-interest communities from banning ADUs, restricting rentals below 25% of separate interests, or treating ADUs as separate HOA interests. Limits remain: HOAs retain authority over reasonable design standards and statutory height limits, and the 2026 Carlsbad case (CalMatters coverage) established that an HOA's documented design-standards regime can effectively delay or constrain ADU approval short of outright prohibition.
State financing programs
California's flagship state-level ADU financing program — the CalHFA ADU Grant Program — is paused and has not been refunded since the original $100 million allocation was fully deployed 2023-12-28. The program provided up to $40,000 per qualifying homeowner for pre-construction and non-recurring closing costs and financed approximately 2,500 ADUs in two rounds. As of 2026-04, no new funding round has been announced in the state budget. CalHFA continues to publish anti-scam warnings because bad actors actively solicit homeowners claiming access to grant funds that no longer exist. State-level financing activity has shifted to local pilot programs (San Francisco, San Jose, Los Angeles, San Diego) and private financing products (Fannie Mae ADU mortgage, HELOC, construction-to-permanent).
State housing programs
California's state-level ADU programs are concentrated at HCD (technical guidance, ordinance review, enforcement) and the paused CalHFA grant pipeline (covered under stateFinancing). The state does not operate a central pre-approved ADU plan library — instead, AB 1332 (2024) created a preemption framework for local pre-approved plans with a 30-day ministerial-approval deadline, and major cities (Los Angeles, San Diego, San Jose, Sacramento, Berkeley) have rolled out their own plan catalogs. The California YIMBY coalition and other housing-policy organizations play an influential role in bill drafting; they are not state agencies but effectively drive much of the ADU legislative agenda. The Title 24 code cycle (now 2025, in effect for 2026 permits) is the authoritative building-code baseline.
Federal (United States) — ADU-relevant rules and programs
Federal ADU law
The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.
Federal financing programs
Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.
Federal tax credits
There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.
Federal housing programs
HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.