Multifamily and Duplex Properties for Sale in Napa County: Zoning and Rent Rules

What multifamily in Napa County looks like

Nearly all of Napa County’s apartment buildings, duplexes and fourplexes are inside its five incorporated jurisdictions: the cities of Napa, American Canyon, Calistoga and St. Helena and the Town of Yountville. The unincorporated County is overwhelmingly agricultural watershed and vineyard land, so income property there usually means a farmhouse with an ADU or guest cottage, farmworker housing, a mobile home park, or one of a small number of sites the County has zoned for multifamily in places like Angwin and Spanish Flat near Lake Berryessa. For two to four units, read financing 2-4 unit properties; for larger buildings, see apartment building loans.

Where the zoning allows it

Inside the cities, city codes control; our City of Napa multifamily page covers the county seat, and we also have pages for American Canyon, Calistoga, St. Helena and Yountville. In unincorporated areas, Title 18 of the Napa County Code applies.

County district	What the code says it is for	Multifamily rules
RM Residential Multiple (Ch. 18.60)	Multifamily housing in established urban areas with public water, sewer and services	Multifamily and SRO units allowed without a use permit; 20 to 25 units per acre; 20% affordable set-aside
AH Affordable Housing combining district (Ch. 18.82)	Specified priority housing sites from the Housing Element	Ministerial approval for qualifying projects in Angwin, Moskowite Corner and Spanish Flat
RS Residential Single (Ch. 18.52)	Single-family neighborhoods	ADU and JADU by state rules
RC Residential Country (Ch. 18.64)	Rural residential	ADU and JADU by state rules
PD Planned Development (Ch. 18.48)	Uses set by an approved plan	Check the plan
AW Agricultural Watershed (Ch. 18.20)	Agriculture and watershed protection	One home, ADUs, a guest cottage and small farmworker housing

The RM district. The RM chapter sets a minimum of 20 and a maximum of 25 units per acre, requires at least 40% of the site as common space and buildings at least 12 feet apart, and requires projects with multifamily or SRO units to reserve 20% for lower-income households. That set-aside is a major underwriting item.

AH sites. The AH chapter lists its eligible sites by name: Angwin Sites A and B (up to 25 units per acre, 191 units combined), Moskowite Corner Sites A through D (up to 10 per acre, 100 combined), and Spanish Flat sites (up to 25 per acre). Projects that meet its affordability and design standards need only a building permit, reviewed ministerially, though they must show sewer and water service, typically with a will-serve letter.

Agricultural land. On AW parcels, the code allows one single-family home per legal lot, ADUs and a JADU, one guest cottage, and farmworker housing for six or fewer employees without a use permit. Under Section 18.104.080, a guest cottage needs an existing legal home, cannot exceed 1,000 square feet or the main home’s living area, and must generally sit within 500 feet of it.

ADUs. The County’s ADU page allows ADUs up to 1,200 square feet and JADUs up to 500, and warns that a permit may be denied for inadequate potable water, groundwater overuse or failing septic. See our ADU investment guide. SB 9 lot splits apply only to qualifying urban single-family lots, which excludes most of the County’s agricultural land.

Housing Element. The Board certified the Housing Element Update EIR for 2023-2031 on January 24, 2023, according to the state notice of determination, and the County announced state certification on July 12, 2024, with rezoning of the Foster Road and Spanish Flat sites complete.

Rent rules: state law only in unincorporated Napa County

The Attorney General’s rent cap page, updated July 16, 2026, places Napa County in All Other Counties: 7.7% for increases from August 1, 2025 and 8.6% for increases from August 1, 2026 through July 31, 2027. No Napa County jurisdiction appears on its chart of local rent ordinances. Covered units also follow state just cause rules. Read our AB 1482 guide and just cause eviction guide.

Napa County rental property rules

No transient rentals in homes. Napa County Code Section 18.104.410 prohibits transient commercial occupancy of dwelling units in every residential and agricultural district. This is the biggest difference from many wine-country counties: a farmhouse or cottage in unincorporated Napa cannot be bought as a vacation rental.

ADU covenant. Under Section 18.104.180, owners must acknowledge in writing that neither the ADU nor the main home may be rented for less than 30 days, and record a covenant to that effect before the building permit issues.

Bed and breakfasts. Section 18.104.050 allows B&Bs only where a district expressly permits them, with guest registers kept three years and transient occupancy tax paid.

Water, septic and agricultural limits

Outside the cities, wells and septic systems decide how many units a parcel can carry. The County’s ADU page lists groundwater overuse and undersized septic among reasons to deny a permit, and the RM and AH chapters assume public water and sewer. In the AW and AP districts, the Section 18.104 rules set a two-acre minimum for farmworker centers. For buildings with three or more units and elevated decks, plan for SB 721 balcony inspections, and for older wood-frame buildings consider a seismic retrofit review.

Underwriting a Napa County multifamily purchase

Confirm whether the parcel is in one of the five cities or unincorporated, then read the County district.
On RM land, account for the 20% lower-income set-aside and 40% common space.
On AH sites, confirm the site is named in Chapter 18.82 and that sewer and water will serve.
On agricultural parcels, inspect wells and septic before counting an ADU or guest cottage as income.
Underwrite long-term rents only, model increases at or below 8.6%, and obtain estoppel certificates.
Rebuild expenses with reassessed taxes in our rental property analysis.

Questions people ask

Is there rent control in Napa County?

No local rent control appears on the Attorney General’s chart for any Napa County jurisdiction. AB 1482 caps apply to covered units, at 8.6% from August 1, 2026.

Can I use a cottage in unincorporated Napa County as a vacation rental?

No. County Code Section 18.104.410 bars transient commercial occupancy of dwellings in all residential and agricultural districts.

Which County zone allows apartments?

RM, at 20 to 25 units per acre, plus the AH combining district on named Housing Element sites.

Do County multifamily projects require affordable units?

RM projects with multifamily or SRO units must reserve 20% for lower-income households.

Can I add an ADU on vineyard land?

Generally yes in the AW district, subject to County ADU rules, a no-short-term-rental covenant and adequate water and septic.

Where are the County’s new housing sites?

The AH chapter names sites in Angwin, Moskowite Corner and Spanish Flat, and the County reported Foster Road and Spanish Flat rezoning complete in 2024.

Sources & notes

General information, not legal or tax advice. Last reviewed October 2026 by Matthew Martinez.

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