3 county-level rules, plus city-specific rules for 1 city in Napa County, California.
Verified from official government sources
Napa County Code Section 18.104.180 ministerially permits Accessory Dwelling Units (ADUs, called 'second units') and Junior ADUs (JADUs) on legal lots zoned RS, RC, AW, or PD, with a 1,200 sq ft maximum for ADUs (500 sq ft for JADUs) and four-foot side/rear setbacks for new detached units up to 16 feet tall.
Napa County Code § 18.104.180 (Junior accessory dwelling unit and second unit), as amended by Ordinance 1456 (2020)
A. Pursuant to the provisions of Government Code Sections 65852.2 and 65852.22, the following requirements apply to all second units and junior accessory dwelling units, as applicable: 1. The lot is a legal lot as defined by Section 18.08.340 of this title. 2. The lot is zoned RS, RC, AW, or PD when the lot contains an existing or proposed single family dwelling or existing multifamily unit tha...
Per the California Building Code section 105.2 (adopted via Napa County Code Title 15, Chapter 15.12), one-story detached storage sheds with a floor area of 120 sq ft or less are exempt from a building permit, but zoning setbacks under Napa County Code Title 18 (including the four-foot side/rear standard for accessory buildings on lots under 60 feet wide) still apply.
Napa County Code Compliance - ADU Delayed Enforcement Program Inspection Checklist (Yard & Outdoor Areas; Zoning & Land Use)
Yard & Outdoor Areas: Yards are sanitary, free of garbage, debris, overgrowth, or excessive storage. No dismantled/inoperable vehicles stored on site. Storage sheds, patio covers, and accessory structures are maintained and structurally sound. ... Zoning & Land Use (Check All That Apply): A primary residence exists (or is proposed) on the parcel. ADU complies with required setbacks (4' side/rea...
Napa County Code Section 18.104.180 (per Ordinance 1456) expressly defines a 'second unit, detached' to include a second unit located within a detached garage or other accessory structure, and section 18.104.180(A)(12) provides that no replacement parking spaces are required when an existing garage, carport, or covered parking is replaced by a second unit.
Napa County Code §§ 18.08.550(B), 18.104.180(A)(12), 18.104.180(A)(16)(a) (as amended by Ordinance 1456)
B. 'Second unit, detached' means a second unit that is not attached to or located within a proposed or existing primary dwelling unit, including a second unit attached to, or located within, a detached garage, outbuilding, or other accessory structure. ... 12. If the construction of a second unit replaces an existing garage, carport, or covered parking structure, no replacement spaces need be p...
1 cities in Napa County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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