Napa County

Napa ADU rules

Research summary of local ADU rules on file for Napa in Napa County. Not a determination for a specific lot.

Last checked October 26, 2026.

City or county ADU page

Napa rules on file

Local rules recorded in this project for this jurisdiction. Where a city figure on file is stricter than the state baseline on file, both are shown.

Which rules apply
The City of Napa's ADU rules are in Municipal Code Section 17.52.015 (last amended by Ordinance O2025-013, September 2, 2025). Its attached-ADU size cap and its owner-occupancy rule for junior ADUs are left out of this summary because they may conflict with state law; state rules apply to those items.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015, accessed 2026-10-25.

Review
Each ADU or junior ADU needs an ADU or junior ADU building permit, reviewed ministerially by the Director. Properties on the City's Historic Resources Inventory need historic clearance, within the limits of Gov. Code 66323. No certificate of occupancy for an ADU before the main home's.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(B), accessed 2026-10-25.

How many units
As many ADUs and junior ADUs as Gov. Code 66323(a)(1)-(4) allows, plus one bonus ADU for each ADU kept affordable to very low or low income households for at least 10 years. A detached ADU of 800 sq ft is allowed on a lot with a main home. No minimum lot size.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(C)(1), accessed 2026-10-25.

Detached ADU size
Up to 1,200 sq ft, except conversions. Conversions may not exceed the existing structure except up to 150 sq ft for entry.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(C)(2)(a), (c), accessed 2026-10-25.

Coverage and setbacks
Zone coverage limits apply unless they would prevent an 800 sq ft ADU. 4 ft side and rear setbacks except conversions and same-footprint rebuilds. The zone's front setback applies unless it would prevent an 800 sq ft ADU.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(C)(3)-(4), accessed 2026-10-25.

Height
Up to the heights in Gov. Code 66321(b)(4), and no more than two stories. Second-story units must face entries, stairs and balconies away from the nearest residential lot line and use clerestory or privacy glass (or fencing or landscaping) for windows facing neighbors.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(C)(5), (8), accessed 2026-10-25.

Fire sprinklers
Not required unless required for the main home, and adding an ADU or junior ADU does not trigger sprinklers in an existing home.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(C)(7), accessed 2026-10-25.

Junior ADUs
Up to 500 sq ft (a shared bathroom is not counted), with an efficiency kitchen and, if it has no bathroom of its own, an interior door to the home. No parking is required. A deed restriction against separate sale is recorded before occupancy.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(C)(6)(c), (C)(9), (D)(3), (F)(4), accessed 2026-10-25.

Parking
One off-street space per ADU except where Gov. Code 66322 and 66323 say none is required. No replacement parking when a garage or carport is converted or removed for an ADU.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(D)(1)-(2), accessed 2026-10-25.

Utilities and fees
No new utility connection for attached ADUs or junior ADUs (unless built with a new home). No impact fees for junior ADUs or ADUs under 750 sq ft; larger ADUs pay in proportion to the main home.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(E), accessed 2026-10-25.

Rentals and sale
Rentals must be longer than 30 days. No ADU may be sold separately except as Gov. Code 66341 allows.
Source: Napa Municipal Code Sec. 17.52.015 Accessory dwelling units and junior accessory dwelling units (eCode360; as amended by Ord. O2025-013, Sept. 2, 2025), Sec. 17.52.015(F)(2)-(3), accessed 2026-10-25.

Where to ask
City of Napa Planning Division. The City's ADU page has its ADU information.
Source: City of Napa, Accessory Dwelling Units page, accessed 2026-10-25.

California state rules on file

The statewide baseline recorded from state law and the HCD ADU Handbook.

Detached size cap described in state law
1,200 sq ft. Recorded in this rules file from Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Side and rear setback cap for a new ADU
4 ft. Recorded in this rules file from Government Code section 66314, which describes a cap on side and rear setbacks for a new ADU.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Setback for a conversion of an existing structure
No additional setback, as recorded in this rules file from Government Code section 66314 for a conversion of an existing structure.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Minimum lot size
A city may not impose a minimum lot size for an ADU, as recorded in this rules file from Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Minimum unit the handbook says cities must allow
At least an 800 sq ft ADU with 4 ft side and rear setbacks. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(3).
Source: HCD ADU Handbook, 66321(b)(3); handbook updated March 2026, accessed 2026-10-16.

Detached height described in the handbook
16 ft, or 18 ft or 20 ft in some cases. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(4).
Source: HCD ADU Handbook, 66321(b)(4); handbook updated March 2026, accessed 2026-10-16.

Permit decision deadline
60 days. Recorded in this rules file from Government Code section 66317(a)(3): the permitting agency must decide on (approve or deny) a completed ADU application within 60 days when an existing single-family or multifamily dwelling is on the lot. Section 66317(a)(1) says the application is considered ministerially, without discretionary review or a hearing.
Source: California Government Code section 66317, 66317(a)(1), (a)(3), accessed 2026-10-17.

Owner-occupancy requirement
None. Recorded in this rules file from Government Code section 66315: a local agency may not impose an owner-occupancy requirement on an ADU. It may require that the property be used for rentals of terms 30 days or longer. The HCD ADU Handbook (updated March 2026) describes the same rule.
Source: California Government Code section 66315, 66315; HCD ADU Handbook updated March 2026, accessed 2026-10-17.

Parking near public transit
No parking standards within one-half mile walking distance of public transit. Recorded in this rules file from Government Code section 66322(a)(1). Section 66322(a) lists several other cases where parking standards may not be imposed.
Source: California Government Code section 66322, 66322(a), accessed 2026-10-17.

Ministerial categories
The HCD ADU Handbook (updated March 2026) states that Government Code section 66323 sets four ministerial categories. This rules file does not restate those four categories.
Source: HCD ADU Handbook, 66323; handbook updated March 2026, accessed 2026-10-16.

Fire Hazard Severity Zones
If your lot is in a Fire Hazard Severity Zone, the CAL FIRE Office of the State Fire Marshal says in Information Bulletin 25-004 (issued March 3, 2025): “Fire Hazard Severity Zones (FHSZs) should not restrict the development of Accessory Dwelling Units (ADUs). However, additional building standards may be necessary, including but not limited to California Fire Code Chapter 49 and California Building Code Chapter 7A.” State ADU law does not itself bar an ADU there. A city or county may still apply its building code, including wildfire-resistant construction (Gov. Code 66314(d)(8)); require side and rear setbacks “sufficient for fire and safety” for a unit converted under 66323(a)(1); and decline parking in setbacks on specific fire and life safety findings (66314(d)(10)(B)). It may also consider public safety when it designates where ADUs may be permitted (66314(a)). Sprinklers can't be required in an ADU or JADU if the primary residence doesn't need them (66314(d)(12), 66323(d)). Some cities and counties still apply their own fire-zone limits. Where this summary has one, it is listed with the local rules. This summary does not look up your lot. Check the CAL FIRE Fire Hazard Severity Zone map viewer linked from the State Fire Marshal's Fire Hazard Severity Zones page: https://experience.arcgis.com/experience/5065c998b4b0462f9ec3c6c226c610a9
Source: CAL FIRE Office of the State Fire Marshal Information Bulletin 25-004, page 4, issued March 3, 2025; Gov. Code 66314, 66323, accessed 2026-10-20.

State baseline on the directory → · State ADU rules on the homepage →

Can I build an ADU in Napa?

State law sets a baseline for ADUs in Napa, and the local standards on file are listed on this page. Whether a specific lot can add an ADU depends on zoning, utilities, and other site facts this page does not measure. Confirm with the City of Napa Planning Division, or run a free address summary.

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