Elmira

Solano County is a population ~455,000 county on the northeastern edge of the San Francisco Bay Area, occupying the corridor between the Carquinez Strait / Suisun Bay (south), Napa County (west), Yolo County (north), and Sacramento County / the Sacramento River (east). The seven incorporated cities are Vallejo (~125,000, the county's largest, on the Carquinez Strait facing Mare Island), Fairfield (~120,000, the county seat, in central Solano along I-80 and adjacent to Travis AFB), Vacaville (~103,000, in eastern Solano along I-80 between Fairfield and Sacramento), Suisun City (~30,000, on the Suisun Marsh waterfront), Benicia (~28,000, on the Carquinez Strait facing Martinez), Dixon (~20,000, in agricultural eastern Solano), and Rio Vista (~10,000, on the Sacramento River in the Delta). The Board of Supervisors administers ADUs in unincorporated areas under Cal. Gov. Code Sec. 65852.2 / 65852.22 via the County Department of Resource Management. Solano is a member of the Association of Bay Area Governments (ABAG) and the Metropolitan Transportation Commission (MTC) and is subject to RHNA 6th-cycle (2023-2031) housing allocations administered through the regional Plan Bay Area 2050 framework. The county has substantial unincorporated population including the Cordelia / Green Valley corridor (Fairfield-adjacent), the Elmira / Allendale / English Hills agricultural belt (Vacaville-adjacent), Suisun Valley (a small AVA wine region in the Vaca Mountains foothills), and the Collinsville / Birds Landing / Montezuma Hills wind-energy corridor (eastern Solano along the Sacramento River). The county-wide character is hybridized between dense Bay Area urban (Vallejo / Benicia along the Carquinez Strait, Fairfield / Vacaville along I-80) and the Sacramento Valley agricultural / floodplain belt (Dixon / Rio Vista / the Yolo Bypass periphery). The Suisun Marsh covers the southern third of the county and is the largest contiguous brackish-water wetland in the western US, regulated by the Suisun Marsh Preservation Act.

• Solano County Code Title 28 (Zoning), ADU/JADU provisions
• Cal. Gov't Code Sec. 65852.2 (Accessory Dwelling Units)
• Cal. Gov't Code Sec. 65852.22 (Junior Accessory Dwelling Units)
• Suisun Marsh Preservation Act of 1977, Pub. Resources Code Sec. 29000 et seq.
• McAteer-Petris Act / San Francisco Bay Conservation and Development Commission (BCDC), Gov. Code Sec. 66600 et seq.
• Solano County General Plan 2008 (with 2023 Housing Element 6th Cycle update)

State-floor overlay: California state ADU preemption applies in full to unincorporated Solano County. AB 1033 condo-conversion election: not adopted as of April 2026. AB 976 prohibits owner-occupancy mandates on detached ADUs. AB 2533 unpermitted-ADU amnesty applies. SB 9 urban lot-split provisions apply only within incorporated cities; they do not apply in unincorporated parcels which are zoned A-160 / A-40 / A-20 (agricultural) for the bulk of the county. HCD oversight applies to ordinance amendments per Sec. 65852.2(h); Solano's 2023 housing element was conditionally certified and the unincorporated sub-jurisdiction has been responsive to HCD comments. Travis AFB AICUZ overlay applies to a corridor extending several miles east, west, and south of the runway centerline; ADUs within AICUZ Zones I-III face noise-attenuation construction requirements per AFI 32-7064. Suisun Marsh Primary Management Area effectively prohibits new residential construction including ADUs.

Solano County overlays of consequence are defined by four large structural features: (1) Travis AFB and its AICUZ overlay; (2) the Suisun Marsh Preservation Act / BCDC jurisdiction covering the southern third of the county; (3) FEMA SFHA along the Sacramento River, Suisun Slough, Putah Creek, and Carquinez Strait shoreline; and (4) the Solano HCP / Solano Subregional Habitat Conservation Plan covering listed-species habitat across the agricultural belt. CAL FIRE SRA Very High FHSZ applies in the Vaca Mountains, Cherry Glen, and portions of Suisun Valley and English Hills. The Sacramento-San Joaquin Delta Plan applies to the eastern county. The Bay Area Air Quality Management District applies county-wide for construction-emissions compliance. Williamson Act ag-preserves cover the bulk of unincorporated agricultural Solano. ABAG / MTC RHNA 6th-cycle housing allocations apply to all jurisdictions in the county.

• Travis AFB Air Installation Compatible Use Zone (AICUZ)
• Suisun Marsh Preservation Act / BCDC Suisun Marsh Primary and Secondary Management Areas
• Sacramento-San Joaquin Delta Plan / Delta Stewardship Council jurisdiction
• FEMA SFHA - Sacramento River, Suisun Slough, Putah Creek, Carquinez Strait shoreline, Bay tributaries
• CAL FIRE State Responsibility Area / Vaca Mountains Very High FHSZ
• Solano Subregional Habitat Conservation Plan (Solano HCP)
• Williamson Act / Land Conservation Act agricultural preserves
• ABAG / MTC RHNA 6th Cycle (Plan Bay Area 2050)
• Bay Area Air Quality Management District (BAAQMD)

Solano County Department of Resource Management (Planning Services Division and Building Division) issues ADU permits for unincorporated parcels including the Cordelia / Green Valley / Suisun Valley AVA corridor, the Elmira / Allendale / English Hills agricultural belt, Collinsville / Birds Landing / Montezuma Hills, the Dixon / Davis-adjacent agricultural fringe, and the Rio Vista / Delta periphery. Practical permitting frictions: Travis AFB AICUZ (Air Installation Compatible Use Zone) overlay covering a broad corridor surrounding the runway and approach paths; Suisun Marsh Preservation Act jurisdiction (Primary Management Area effectively prohibits new residential construction; Secondary Management Area carries BCDC review); FEMA Special Flood Hazard Area along the Sacramento River, Suisun Slough, Putah Creek, and various Bay tributaries; CAL FIRE State Responsibility Area in the Vaca Mountains and English Hills (Very High FHSZ in portions of Suisun Valley and Cherry Glen); the Sacramento-San Joaquin Delta Plan jurisdiction in the eastern county (Rio Vista / Brannan-Andrus Island vicinity); the Solano Subregional Habitat Conservation Plan (Solano HCP) covering Swainson's hawk, giant garter snake, valley elderberry longhorn beetle, and tiger salamander habitats; the Solano Land Trust and Solano Open Space Conservation Easements covering ~17,000 acres; Williamson Act (Land Conservation Act) parcels covering the bulk of agricultural Solano; and the Bay Area Air Quality Management District (BAAQMD) jurisdiction for construction-emissions and VOC compliance.