Multifamily and Duplex Properties for Sale in The Springs: Zoning and Rent Rules

What multifamily in The Springs looks like

The Springs, the unincorporated area of Boyes Hot Springs, Fetters Hot Springs and Agua Caliente north of the City of Sonoma, holds much of Sonoma Valley’s workforce rental housing. Expect older duplexes and fourplexes on the side streets, small apartment buildings and cottage courts near Highway 12, houses with second units, and mobile home parks. Rules here are the County’s, not the city’s, and that difference drives both tenant law and what can be built. For two to four units, read financing 2-4 unit properties; for five or more, see apartment building loans.

Where the zoning allows it

Article 08 of the County zoning code, adopted in 2021 and last amended by Ordinance 6532 in October 2025, sets residential zones. The Official Zoning Database shows each parcel’s zone.

R3’s unit-size math. Because small units count as fractions of a unit, an R3 site can hold more studios than its headline density suggests. Check the table before you value a site.

The Springs Specific Plan. Permit Sonoma’s plan page describes a draft plan covering about 178 acres along Highway 12 that would rezone for mixed residential and neighborhood commercial uses and create room for more than 700 homes. The state CEQA record puts buildout at about 706 units. The draft EIR circulated in 2022 and is being revised, and no adoption is recorded, so value land on current zoning.

ADUs and SB 9. Permit Sonoma’s streamlined housing page explains that SB 9 applies in single-family zones within a Census urban area, screened with its PJR-142 checklist. The County’s census urban area layer shows a Sonoma urban cluster with about 6,474 acres outside city limits, which likely takes in parts of the Springs. Check each lot. See our SB 9 lot split guide and ADU investment guide.

Rent rules: state rent cap plus County tenant protections

AB 1482. The Attorney General’s rent cap page, updated July 16, 2026, puts Sonoma County under "All Other Counties," with covered units allowed up to 8.6% for increases from August 1, 2026 through July 31, 2027. There is no local rent cap.

County Ordinance 6496. Because the Springs is unincorporated, landlords follow the County’s Residential Tenancy Protections Ordinance, passed 3-1 on September 17, 2024 and effective about 30 days later. A landlord buying just across the city line takes on obligations a city landlord does not.

• Just cause from the start. Protections begin when lawful occupancy starts, not after the state’s 12 months.
• Nonpayment. It counts as just cause only when more than one month’s rent is owed, and tenants can use that defense twice a year.
• Relocation. A no-fault termination requires the greater of HUD Fair Market Rent for the Santa Rosa area or the actual rent.
• Portal filing. Termination notices served from January 1, 2025 must be filed on the County portal within three days, as the landlord page explains.
• Affordable units. Deed-restricted affordable units are brought under the rules.
• Rent levels. It does not cap rents.

See our AB 1482 guide and just cause eviction guide.

The Springs rental property rules

• Vacation rentals. Permit Sonoma does not allow vacation rentals in R1, R2 or R3, in ADUs or in farmworker housing. Section 26-08-050 also bars transient stays in multifamily projects of four or more units. Underwrite Springs rentals as long-term housing.
• Mobile home parks. Parks are allowed by use permit in R1, R2 and R3. We did not verify County space rent rules for parks here.
• Transfer tax. Only the County’s $0.55 per $500.

Sewer, water and older buildings

Sewer. The Sonoma Valley County Sanitation District bills per equivalent single-family dwelling, and its 2026 newsletter proposed $1,514 a year per ESD from July 1, 2026. Sewer cost scales with unit count, so confirm the ESDs assigned to the parcel. The district reports a multi-year pumping and piping upgrade at its plant.

Water. Permit Sonoma’s referral list names Valley of the Moon Water District for Boyes Hot Springs and El Verano.

Buildings. Much Springs stock is older wood frame, some once seasonal resort cottages. Get a seismic retrofit review for raised or tuck-under buildings, and budget SB 721 balcony inspections for three or more units with elevated decks.

Underwriting a Springs multifamily purchase

1. Confirm the parcel is unincorporated; the tenant rules change at the city line.
2. Classify units under AB 1482 and Ordinance 6496, and model increases at or below 8.6% for covered units.
3. Budget relocation at the greater of HUD Fair Market Rent or actual rent for any planned no-fault termination.
4. Verify legal unit count with Permit Sonoma and ESDs with Sonoma Water; older cottage courts may exceed today’s density.
5. Collect leases, the rent roll, County portal filings and estoppel certificates.
6. Rebuild expenses with reassessed taxes, per-unit sewer charges, insurance and SB 721 in our rental property analysis.

Questions people ask

Sources & notes

1. County Code Article 08 and Article 10
2. Permit Sonoma, Springs Specific Plan and CEQAnet, SCH 2018062068
3. Ordinance 6496 and landlord page
4. California Attorney General, rent caps
5. Permit Sonoma, vacation rentals
6. Sonoma Valley County Sanitation District newsletter, 2026
7. Permit Sonoma water and sewer referral list
8. Sonoma County Recorder, documentary transfer tax

Note: The census layer does not name the Springs, so whether a given lot is in the Sonoma urban cluster is not confirmed. We did not verify mobile home space rent rules or confirm each parcel’s sanitation district connection. The housing stock description is a general observation. See also our Sonoma County multifamily guide and Sonoma County commercial guide.

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

Related: The Springs real estate guide · Commercial real estate in The Springs · Multifamily investing guide · Investor services