Sonoma County Multifamily Properties for Sale: Duplexes to Apartments
Multifamily property in Sonoma County means duplexes, triplexes and fourplexes as well as larger apartment buildings, and it is concentrated in zones that allow more than one home per lot, such as Santa Rosa’s R-2 and R-3 districts. Before you price a duplex in Santa Rosa or a fourplex in Petaluma, find out which rules apply: the state’s AB 1482 rent cap and just cause law, Petaluma’s own tenant ordinance, or, outside city limits, the county’s Ordinance 6496. Those rules, the rent roll and the transfer tax shape the deal more than the listing price does.
This page is the Sonoma County part of our multifamily investing guide. It covers where multifamily zoning exists, how tenant rules differ between Santa Rosa, Petaluma and unincorporated areas, transfer tax, inspections specific to apartment buildings, and a checklist for underwriting a purchase. For the county as a whole, see our Sonoma County real estate guide.
Sonoma County homes for sale
Sonoma County market report
What you will find for sale
Listings range from duplexes and fourplexes on standard city lots and older houses divided into units to small courtyard buildings and larger apartment complexes. The smaller properties compete for buyers with single-family homes, because an owner can live in one unit and rent the others.
Size changes the deal. Two- to four-unit properties are usually bought with residential-style financing, while larger buildings are underwritten on their income; our guides to financing 2-4 unit properties and apartment building loans explain the difference. A duplex where the owner lives in one unit can also carry a special status under state tenant law, covered below.
Where multifamily zoning exists
In Santa Rosa, the city’s zoning map ties each district to a General Plan land use class. Under Table 2-1 of the zoning code, the R-2 district implements the Medium Density residential class, R-3 implements Medium and Medium High Density, and MH implements Mobile Home Parks.
R-1 implements the lower-density classes. Those R-2 and R-3 parcels are where you will find most of the city’s purpose-built multifamily.
State housing law also loosens the link between zoning and the General Plan. Santa Rosa’s code says a housing project that meets objective General Plan standards does not have to rezone the site for consistency, and must instead meet the standards of the district that implements that General Plan class. For investors thinking about adding units, see our guide to ADUs on multifamily properties.
Petaluma, Rohnert Park and the other cities each have their own zoning codes, and unincorporated land is zoned by the county. Check the zoning and any recorded conditions for the specific parcel with the city or county planning counter before you assume an extra unit is legal. A building with more units than its permits show is a different risk; ask for the permit history.
Tenant rules by jurisdiction
State law is the baseline. AB 1482 caps rent increases on covered units and, after a tenant has lived there 12 months, requires a just cause to end the tenancy.
Two exemptions matter most for small multifamily: housing whose certificate of occupancy was issued within the previous 15 years, and two units in one structure where the owner lived in one unit when the tenancy began and still does, provided neither is an ADU or JADU. Our AB 1482 guide has this year’s cap.
| Jurisdiction | Rent cap | Just cause starts | No-fault relocation |
|---|---|---|---|
| Santa Rosa | State cap where it applies | State rule: after 12 months | State rule: one month’s rent or a waiver of the last month |
| Petaluma (Chapter 6.60) | State cap where it applies | First day of the tenancy | 250% of one month’s rent or $9,000, whichever is less |
| Unincorporated Sonoma County (Ordinance 6496) | State cap where it applies | Start of the tenancy | The greater of HUD Fair Market Rent or the actual monthly rent |
Santa Rosa
Santa Rosa’s city council adopted a rent stabilization ordinance in 2016, but voters rejected Measure C, which would have kept it, in a June 6, 2017 special election, with 52.5% voting no. For a Santa Rosa apartment, plan on the state rules unless the city has adopted something since; confirm with the city before you close. Our Santa Rosa investment property guide covers the city’s rental market.
Petaluma
Petaluma’s Residential Tenancy Protections took effect October 12, 2022, and were amended effective June 15, 2023. Protection starts on the first day of a tenancy. Owners of three or fewer units are exempt unless they are a REIT, a corporation or an LLC with a corporate member, and exempt owners must give tenants a written notice.
Landlords must also give tenants the city’s Notice of Tenant Rights at set times, including before selling a rental and within 30 days of acquiring one. See our Petaluma guide for the city’s other rules.
Unincorporated areas
Ordinance 6496, adopted September 17, 2024, applies to rentals outside city limits, such as Larkfield, the Springs and rural West County. It starts just cause at move-in, removes the state exemption for deed-restricted affordable housing, and raises no-fault relocation.
Landlords must file a copy of every termination notice served on or after January 1, 2025 on the county’s portal within three days of serving it, whether or not state law covers the tenancy, and notices must state that the sale of the property is not a valid ground for eviction. The ordinance sets no rent cap.
Several Sonoma cities also limit space-rent increases in mobilehome parks; that is a separate set of rules, covered in our Sonoma County mobile homes guide.
Transfer tax on a Sonoma County sale
The county’s documentary transfer tax is $0.55 per $500 of value, less any loans assumed. Santa Rosa and Petaluma each add $2.00 per $1,000, with no exemption for assumed loans. The County Recorder lists Cloverdale, Cotati, Healdsburg, Rohnert Park, Sebastopol, Sonoma and Windsor at the county rate only.
On our arithmetic, a $1,500,000 fourplex in Santa Rosa would pay $1,650 to the county and $3,000 to the city, $4,650 in all. In Diamond’s North Bay markets the seller customarily pays, but it is negotiable and local custom varies, so settle it in the purchase contract.
Inspections and records specific to apartment buildings
- Balconies and stairs (SB 721). Buildings with three or more multifamily units must have wood-supported balconies, decks, stairways and walkways more than six feet above ground inspected, first by January 1, 2026 and then every six years. Reports must be kept for two inspection cycles and given to the buyer at a sale, so ask for them. Our SB 721 guide explains the repair deadlines.
- Permits and unit count. Compare the number of units on the rent roll with the permits and the assessor’s record.
- Utilities. Find out which units are separately metered for gas, electricity and water, and who pays water, sewer and garbage under each lease. Owner-paid utilities come straight out of net income.
- Insurance. Get quotes early, especially for older wood-frame buildings and anything in a mapped fire hazard area, because the premium can change the price you can pay.
Underwriting checklist for a Sonoma County multifamily purchase
- Confirm the jurisdiction: city or unincorporated county, because that decides which tenant ordinance applies.
- Read every lease against the rent roll and the past 12 months of increases; see our guide to tenant estoppel certificates.
- Test each exemption the seller claims: certificate of occupancy date, owner-occupied duplex status, the written exemption notices.
- Ask for notices served, and in unincorporated areas the county portal filings.
- Model income at current, lawful rents and realistic expenses; our rental property analysis guide walks through it.
- Plan for property tax reassessment at your purchase price, not the seller’s tax bill.
- Decide how you will take title before you sign, since the owner type can affect exemptions.
If you are buying with tenants in place, our guide to buying property with tenants covers deposits, notices and move-in limits. If you plan to live in one unit, see house hacking in the North Bay.
This is general information, not legal or tax advice; talk to a California landlord-tenant attorney or tax adviser about a specific property.
Questions people ask
Does Santa Rosa have rent control?
Not on apartment rents. Voters rejected Measure C in June 2017, which would have kept the city’s rent stabilization ordinance, so the state’s AB 1482 cap applies where it covers the unit. Confirm current city rules before you buy.
Does Petaluma have rent control?
Petaluma has no local cap on rent amounts, but its Chapter 6.60 requires just cause from the first day of a tenancy and relocation for no-fault terminations, with an exemption for qualifying owners of three or fewer units.
What is Sonoma County Ordinance 6496?
It is the county’s tenant protection ordinance for unincorporated areas, adopted September 17, 2024. It starts just cause at move-in, raises no-fault relocation to the greater of HUD Fair Market Rent or actual rent, and requires termination notices to be filed with the county within three days.
Is an owner-occupied duplex exempt from AB 1482?
It can be. State law exempts two units in one structure where the owner lived in one unit when the tenancy began and still does, as long as neither unit is an ADU or JADU. Local ordinances may still apply.
How much is the transfer tax on a Santa Rosa duplex?
The county charges $0.55 per $500 of value, less assumed loans, and Santa Rosa adds $2.00 per $1,000. On a $1,000,000 sale that is $1,100 plus $2,000, or $3,100, on our arithmetic.
Do small apartment buildings need balcony inspections?
Yes, if they have three or more multifamily units and wood-supported balconies, decks or stairs more than six feet above ground. The first inspection was due by January 1, 2026, then every six years.
Where is multifamily zoning in Santa Rosa?
Mostly in the R-2 and R-3 districts, which implement the General Plan’s Medium and Medium High Density residential classes. Check the zoning map for the specific parcel.
If you are shopping for a duplex, fourplex or apartment building in Sonoma County, we can help you check the zoning, tenant rules and rent roll before you write an offer. Contact us to talk through a property or your search. Diamond may refer you to partners we work with, such as lenders or property managers; you’re free to choose any provider.
Sources & notes
- City of Santa Rosa Zoning Code: Chapter 20-20, Zoning Map and Table 2-1 (eCode360)
- Planetizen: Opponents of rent control claim victory in Santa Rosa special election (June 2017)
- City of Petaluma: Tenant rights
- County of Sonoma: Ordinance No. 6496, Residential Tenancy Protections (September 17, 2024)
- County of Sonoma: Residential Tenancy Protections Ordinance, information for landlords
- California Public Law: Civil Code section 1946.2 (just cause and exemptions)
- County of Sonoma Clerk-Recorder: Documentary transfer tax
- California Public Law: Health and Safety Code section 17973 (balcony and deck inspections, SB 721)
Last reviewed October 2026 by Matthew Martinez.
