Multifamily and Duplex Properties for Sale in Castro Valley: Zoning and Rent Rules

What multifamily in Castro Valley looks like

Castro Valley is mostly single-family hills and valley neighborhoods, but it has a real apartment stock close to the center. Garden apartments and small complexes cluster around Castro Valley Boulevard, Redwood Road and Lake Chabot Road. Duplexes and fourplexes sit on the flatter blocks near the BART station and along the I-580 side of the Boulevard. Mobile home parks have long been part of the downtown mix. When the county adopted the central business district plan in 1993, it counted about 1,800 homes in the plan area, roughly 350 of them mobile home spaces. Because Castro Valley is unincorporated, Alameda County sets the zoning and the tenant rules. For financing, see financing 2-4 unit properties and apartment building loans.

Where the zoning allows it

Castro Valley has its own residential districts in Chapter 17.51, adopted in December 2020 to carry out the Castro Valley General Plan. Some areas still carry the countywide R-2 district.

In RSL, RMF and RMX, projects of five or more units need county site development review. R-2 projects in Castro Valley must follow the county’s Residential Design Standards and Guidelines for the West County unincorporated communities. Where those guidelines are silent, the zoning ordinance applies.

Downtown housing. The CBD Specific Plan welcomes high-density housing where it supports commerce. Homes go on upper floors or at the rear of larger parcels on the Boulevard and Redwood Road, and are barred in the intensive retail core. Plan Goal N calls for housing for small and senior households near shops and BART.

Hillsides. The H-O overlay raises the minimum lot size from 5,000 to 10,000 square feet as slope increases, which limits added units in the hills.

See our ADU investment guide and SB 9 lot split guide for adding units to single-family lots.

Rent rules: state cap plus county just cause

The Attorney General’s rent cap page lists no local rent cap for Castro Valley or unincorporated Alameda County. Covered units follow AB 1482 at the San Francisco Area rate: 8.8% for increases from August 1, 2026 through July 31, 2027. See our AB 1482 guide.

Castro Valley landlords do face a county eviction ordinance. The county’s tenant protections page says the Board of Supervisors passed the Just Cause for Eviction ordinance on second reading on February 4, 2025, effective March 6, for all unincorporated areas. It uses the same 11 at-fault and 4 no-fault causes as state law. The notice for a no-fault eviction must explain the tenant’s right to relocation assistance and its amount. Every eviction notice must also be sent to the Community Development Agency, and skipping that step gives the tenant a defense. See our just cause eviction guide.

Castro Valley rental property rules

• Mobile home parks. The county’s Mobile Home Space Rent Stabilization Ordinance, updated April 11, 2017 and amended in 2024, limits space rent increases to 4% a year in most cases in unincorporated parks, including Castro Valley’s. Complaints about park conditions go to the State Mobile Home Ombudsman.
• Notice filing. Keep proof that every just cause notice was sent to the county.
• Utilities. CVSan provides sewer service. Its lateral replacement grant guidelines show the district inspects laterals by video, witnesses testing before backfill and requires a CVSan repair permit. Work in a county road also needs a county encroachment permit. Ask CVSan whether any grant is currently funded.

Building issues in Castro Valley

Much of the apartment stock dates from the 1960s and 1970s and is wood frame, often with tuck-under parking. We did not find a mandatory county soft-story program like Berkeley’s or Alameda’s, but lenders and insurers will still ask, so get a seismic retrofit assessment for open-front buildings. Buildings of three or more units with elevated balconies need SB 721 inspections. Hillside parcels add slope and fire access questions.

Underwriting a Castro Valley multifamily purchase

1. Confirm the parcel is unincorporated and identify its district (RSL, RMF, RMX, R-2 or CBD plan subarea).
2. Model increases at the AB 1482 cap for covered units; there is no local apartment cap.
3. Review any recent terminations and confirm notices were filed with the county under the just cause ordinance.
4. For a mobile home park, model space rents at the 4% county limit.
5. Get CVSan records on the lateral and plan for inspection and permit steps on any sewer work.
6. Collect leases, rent roll and estoppel certificates, and remember that the only transfer tax is the county’s $0.55 per $500 per the Clerk-Recorder, in our rental property analysis.

Questions people ask

Sources & notes

1. California Attorney General, Rent Caps
2. Alameda County Ordinance Code Chapter 17.51, Castro Valley and Chapter 17.10, R-2 (GoCodebook)
3. Castro Valley Central Business District Specific Plan (1993)
4. Alameda County HCD: Tenant Protections and Mobile Homes
5. Castro Valley Sanitary District, Lateral Replacement Grant Program guidelines (2011/12)
6. Alameda County Clerk-Recorder, Real Property Transfer Tax

Note: The CVSan guidelines are from 2011/12; confirm current lateral rules with the district.

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

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