Multifamily and Duplex Properties for Sale in Sunol: Zoning and Rent Rules

What multifamily in Sunol looks like

Sunol has no apartment complexes. Its rental housing is a handful of older homes, cottages and second units in the downtown area and on rural parcels in the surrounding canyons and valley. In Sunol, "multifamily" realistically means:

• A main house plus one or two ADUs or a JADU
• A rural parcel with a secondary unit, caretaker housing or farm employee housing
• A downtown parcel adding extra units under the SD district’s conditional use rules
• A mixed-use downtown building with an apartment over a shop

Septic capacity, water supply and Measure D, not demand, usually decide how many units a parcel can hold. A two- to four-unit property still qualifies for 2-4 unit financing, but rural appraisals and septic reports add time. Our apartment building loans page covers larger properties elsewhere in the county.

Where the zoning allows it

Downtown units. Chapter 17.17 lets the Planning Commission approve more units on a downtown parcel, at one per 8,000 square feet of the lot’s residential area. Each approval needs design review for fit with Sunol’s historic character. It also needs a letter from Alameda County Environmental Health confirming that an on-site septic system can support the total number of bedrooms. The county’s 2008 staff report estimated the district could hold only about ten additional units in all. Homes are limited to two stories and 25 feet.

ADUs. Under Chapter 17.55, a single-family lot can have one new-construction ADU, one conversion ADU and one JADU. Detached ADUs can reach 850 square feet for one bedroom or 1,200 for two or more. On septic, Environmental Health must approve the ADU as well as the building department. ADUs must rent for more than 30 days, and owner occupancy is required only for a JADU that shares a bathroom with the main house. See our ADU investment guide.

SB 9. SB 9 applies only in single-family residential zones and excludes very high fire hazard zones, farmland and other listed sites. A-zoned and watershed parcels do not qualify. Whether a downtown R-1-B-40 lot qualifies depends on its fire hazard and other site factors, so check with County Planning. See our SB 9 lot split guide.

Rent rules: state cap plus county rules

Unincorporated Alameda County has no apartment rent cap. Covered Sunol rentals follow the statewide cap, which the Attorney General sets for the San Francisco Area region at 6.3% from August 1, 2025, and 8.8% from August 1, 2026 through July 31, 2027. Many Sunol rentals are single-family homes that may be exempt from the state cap if the owner is an individual and gives the required notice. See our AB 1482 guide.

Two county ordinances apply throughout the unincorporated area, including Sunol:

• Rent mediation, Chapter 3.68. Adopted by Ordinance 2024-35, it lets either side request mediation within 21 days of an increase over 5% above base rent, or a second increase within 12 months. If the tenant asks, the increase waits until mediation ends. The landlord must take part in good faith.
• Just cause, Chapter 3.70. Effective March 6, 2025, per the county’s tenant protections page. It covers single-family homes when the landlord owns five or more rental units in the unincorporated county. No-fault evictions require relocation pay of two months’ rent, capped at $10,000, according to the Board agenda text. Termination notices must be filed with the county within three days.

See our just cause eviction guide.

Sunol rental property rules

Business license. The county license tax under Chapter 3.04 charges apartment owners $1.25 per $1,000 of gross receipts. It does not cover an owner of a single home, or of up to two units not counting one the owner lives in. Most small Sunol landlords fall under that exclusion.

Caretaker and farm housing. Agricultural caretaker dwellings need a Planning Director finding of necessity and are usually approved for five years. The unit must be removed or converted when the need ends. They are not a long-term rental play.

Advisory review. Downtown projects go to the Sunol Citizens’ Advisory Council before county decisions.

Septic, water and building issues

Septic is the binding limit on new units in Sunol. The SD district requires the Environmental Health septic letter before extra units can be approved, and ADUs on septic need the same department’s sign-off. Zone 7’s Policy 1985-01 also restricts septic for new commercial uses over the groundwater basin, which matters for any mixed-use plan. Older cottages may need a seismic retrofit review. Any building of three or more units with elevated balconies needs SB 721 inspections. Only the county’s $0.55 per $500 transfer tax applies.

Underwriting a Sunol multifamily purchase

1. Confirm each unit’s permit history. Unpermitted second units are common in rural areas and cannot be counted as legal income.
2. Get a septic inspection and the system’s permitted bedroom count, and check well yield if the parcel is not on a water system.
3. For a downtown parcel, ask Planning whether the lot can add units at one per 8,000 square feet and what the septic letter would require.
4. Classify each unit under state law and the county just cause rules, and model increases at or under the state cap.
5. Collect leases and two years of statements, and get estoppel certificates.
6. Add septic upkeep, insurance and reassessed property tax to your rental property analysis.

Questions people ask

Sources & notes

1. Alameda County Ordinance Code Chapter 17.17, SD District, Chapter 17.06, A Districts and Chapter 17.55, ADUs (GoCodebook)
2. Board of Supervisors letter, Downtown Sunol District (2008)
3. Alameda LAFCo Measure D review (2022)
4. Chapter 3.68, Rental Housing Dispute Resolution and Chapter 3.04, Business License Tax
5. Board of Supervisors, Just Cause ordinance (Feb. 2025) and County HCD, Tenant Protections
6. Zone 7 Policy 1985-01
7. Sunol Citizens’ Advisory Council
8. California Attorney General, Rent Caps and Alameda County Clerk-Recorder

Note: SB 9 eligibility here is our reading of state law, which limits it to single-family zones. We did not verify fire hazard mapping for downtown Sunol parcels.

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

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