Solano County, CA Accessory Structures: ADU Rules (2026)
ADU rules in Solano County, CA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Detached ADU max (R-TC)
- 850 sq ft (1,000 sq ft if 2+ bedrooms)
- Detached ADU max (R-R)
- 1,500 sq ft
- Junior ADU max
- 500 sq ft, inside the home
- Side/rear setback
- 4 feet
- Allowed zones
- R-R and R-TC residential districts
- Sale restriction
- Rentable but not separately saleable
Summary
Unincorporated Solano County allows ADUs and JADUs by right on residential lots in rural residential (R-R) and residential-traditional community (R-TC) districts. The County's ADU ordinance (Ch. 28) follows California state ADU law, with four-foot side and rear setbacks and limited parking demands.
An accessory dwelling unit shall not be established on a lot unless the lot is within an R-R or R-TC zoning district. Minimum setbacks to all property lines shall be at least 10 feet, with additional setback requirements determined by the Solano County Planning Division. An accessory dwelling unit or junior accessory dwelling unit may be rented separate from the primary dwelling but may not be sold or otherwise conveyed separate from the primary dwelling.
Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through Ordinance 1868, passed April 9, 2026).
Full Breakdown
Solano County's ADU standards live in Chapter 28 (Zoning Regulations) and apply only to unincorporated areas. An ADU or junior ADU (JADU) is allowed by right on a lot within a rural residential or residential-traditional community zoning district, or within a residential zoning district. A detached ADU in an R-TC district shall not exceed 850 square feet, unless it has more than one bedroom, in which case the floor area shall not exceed 1,000 square feet; in an R-R district a detached ADU may be up to 1,500 square feet.
An attached ADU may not exceed 50% of the primary dwelling's floor area. A JADU shall not exceed 500 square feet and shall be contained entirely within an existing or proposed single-family dwelling with a separate exterior entrance. Per the code, the setback for an ADU shall be four feet from the side and rear lot lines, and height follows the zoning district tables. ADUs reflect California ADU law (Gov. ), which preempts overly restrictive local rules and applies to counties for unincorporated land. An ADU or JADU may be rented separately but may not be sold separately from the primary dwelling, and may not be rented for terms of 30 days or less.
Violations & Fines
Building or occupying an ADU without required Planning and Building permits, exceeding size limits, encroaching into the four-foot side/rear setback, or short-term renting (under 30 days) can trigger code-compliance enforcement, stop-work orders, and required corrections.
Frequently Asked Questions
Can I build an ADU on my unincorporated Solano County lot?
How big can a detached ADU be?
Sources & Official References
Other rules in Solano County
How Solano County compares: Easiest Cities to Build an ADU·California rules heatmap·Compare Solano County to another location·View the California accessory structures overview
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