ADU Regulations in Napa, California

Zoning

Allowed ADU Types

State law requires cities to allow, on a single-family lot, one ADU converted from existing space, one JADU, and one new detached ADU of up to 800 sq ft. Multifamily lots can add up to 8 detached ADUs (not more than the number of existing units) plus conversions of non-livable space for up to 25% of existing units.

Short-term rental (STR) of ADUs is restricted in many Napa residential zones due to the city's STR ordinance; homeowners should verify STR eligibility before designing an ADU for vacation rental purposes. Long-term ADU rentals are encouraged and serve the winery, hospitality, and healthcare workforce. RL (Residential Low Density) zone applies to hillside areas with additional grading review.

Source: City of Napa: Planning Division · Napa Municipal Code Section 17.52.015 (Chapter 17.52)

Dimensions

Size & Setback Requirements

Setbacks

Hillside lots in the RL zone may be subject to additional grading and drainage review. Historic districts in downtown Napa may have design compatibility requirements for attached ADUs visible from the street. Flood zone properties near the Napa River should verify FEMA flood elevation requirements before siting a detached ADU.

Permitting

Permit Process

Napa's ADU permitting is handled by the Planning Division and Building Division jointly. Wine country prestige and limited housing supply create strong market fundamentals for ADU investment. Applicants near the Napa River should consult the city's flood hazard maps early in the design process.

Infrastructure

Utilities & Requirements

Financials

ADU Costs in Napa

Napa ADU rents are bolstered by the chronic housing shortage for winery and hospitality workers who cannot afford homeownership in this premium market. Long-term rental yields are strong. Note: short-term vacation rental permits for ADUs are subject to city STR licensing, cap limits, and may not be available in all zones.

State Law

California Rules That Apply in Napa

Napa can be more generous than state law but not stricter. These statewide minimums were last reviewed September 30, 2026.

Units per lot

Single-family lots can have one ADU converted from existing space, one JADU, and one new detached ADU (up to 800 sq ft). Multifamily lots can add up to 8 detached ADUs (never more than the number of existing units) plus conversions for up to 25% of existing units. Gov. Code §66323; SB 1211 (2024)

Size

Cities must allow at least an 800 sq ft ADU with 4 ft side and rear setbacks. Local maximums can be no lower than 850 sq ft (studio or one bedroom) or 1,000 sq ft (two or more bedrooms). JADUs are capped at 500 sq ft of interior livable space. Gov. Code §§66321, 66333

Height

Detached ADUs: at least 16 ft; 18 ft within half a mile of major transit (plus 2 ft to match the roof pitch of the main home) or on a lot with a multistory multifamily building. Attached ADUs: 25 ft or the zone height limit, whichever is lower. Gov. Code §66321(b)(4); AB 2221 and SB 897 (2022)

Setbacks

Side and rear setbacks for new ADUs can be no more than 4 ft. Conversions of existing legal structures need no extra setback. Front setbacks cannot block an 800 sq ft ADU. Gov. Code §66314(d)(7); AB 2221 (2022)

Permit timeline

The city has 15 business days to say whether an application is complete, or it is deemed complete. It must then approve or deny a complete application within 60 days, with no public hearing. Gov. Code §66317; SB 543 (2025)

Impact fees

No impact fees on ADUs under 750 sq ft; larger units pay fees proportional to the main home. ADUs and JADUs of 500 sq ft or less are exempt from school impact fees. Gov. Code §66324; SB 543 (2025)

Owner-occupancy

Cities cannot require the owner to live on site for an ADU. For a JADU, owner-occupancy can be required only if the JADU shares a bathroom with the main home. JADUs cannot be short-term rentals. AB 976 (2023); AB 1154 (2025)

Parking

No parking is required for an ADU within half a mile walk of public transit, in a historic district, or for a conversion, and garage parking lost to an ADU does not have to be replaced. Gov. Code §66322

Fire sprinklers

Sprinklers cannot be required in an ADU unless the main home is required to have them. Gov. Code §66314(d)(12)

Pre-approved plans

Every city must offer a program for pre-approved detached ADU plans, and plans matching a pre-approved design must be approved or denied within 30 days. AB 1332 (2023); Gov. Code §65852.27

Selling an ADU

Cities may choose to let owners sell an ADU separately as a condominium. It is a local opt-in, so check whether your city has adopted it. AB 1033 (2023)

Unpermitted ADUs

ADUs built without permits before 2020 can be legalized. Cities cannot deny them for code violations unless the unit is a health and safety hazard, and fees are limited. AB 2533 (2024)