Multifamily and Duplex Properties for Sale in Union City: Zoning and Rent Rules

What multifamily in Union City looks like

Union City’s rental stock includes:

• 1970s and 1980s garden apartment complexes along Alvarado-Niles Road and Decoto Road
• Duplexes and small buildings in the older Decoto and Alvarado neighborhoods
• Townhome communities
• New high-density buildings in the Station District near Union City BART
• Several mobile home parks under a city space rent ordinance

Union City has its own tenant protections, including citywide just cause and rent review. A buyer coming from Fremont or Hayward should not assume the same rules. For financing, see financing 2-4 unit properties and apartment building loans.

Where the zoning allows it

Chapter 18.32 sets the residential districts. The Station District has its own high-density chapters.

In the RM districts, multifamily, attached and semi-detached buildings are permitted. Semi-detached homes need at least 3,000 square feet of lot area. Dwelling groups need a use permit in any district. The SEE and CMUE employment districts allow no housing at all.

Station District. Both station districts set minimum densities, so a low-density project will not conform. SEMU-R requires ground-floor commercial on frontages shown in the Station District Specific Plan, though live/work or amenity space can substitute if the project shows a community benefit. In CSMU, buildings over 250 units must include 300 square feet of shared co-working space.

SB 9. Chapter 18.31 applies in the single-family districts. Each SB 9 unit is allowed at least 800 square feet and no more than 2,000. A lot split can create lots as small as 1,200 square feet and requires a three-year owner-occupancy affidavit. Units must rent for more than 30 days. SB 9 is barred on sites with tenants in the past three years, on sites whose owners withdrew units from rent within 15 years, and on historic properties. See our SB 9 lot split guide.

ADUs. ADUs are governed by Chapter 18.34, which we did not open, and state law. See our ADU investment guide.

Rent rules: state cap, rent review and city just cause

Union City is not on the Attorney General’s list of cities with local rent caps, so covered units follow the statewide cap. For the San Francisco Area region, that is 6.3% for increases from August 1, 2025, and 8.8% from August 1, 2026 through July 31, 2027. See our AB 1482 guide.

Rent review, Chapter 5.55. Operative since October 2, 2017, the rent review ordinance covers almost every rental unit in the city. The exception is units under recorded affordability agreements. It has no age or single-family exemption. Its key rules:

• Notice. Every rent increase notice must include the city’s rent review notice, in the three predominant local languages. Without it the increase is void, and the omission is a complete defense to an eviction for nonpayment.
• Trigger. A tenant can request review within 15 days of an increase that takes rent more than 7% above base rent, alone or combined with other increases in 12 months.
• Process. Conciliation comes first, then mediation before a rent review officer within 60 days.
• Landlord participation. The landlord must acknowledge within 10 business days and attend mediation, or the increase is void.
• Outcome. The officer’s recommendation is not binding, and a request does not delay the increase.

Just cause, Chapter 5.50. Union City adopted citywide just cause rules in 2017 by Ordinance 839-17. They cover single-family homes too, with narrow exemptions such as an owner renting two or fewer bedrooms in their own home. To terminate a tenancy, a landlord must meet several conditions:

• hold a valid city business license and have the unit registered
• have given the tenant-rights notice in three languages
• state a listed ground in the termination notice

Listed grounds include nonpayment, material breach, owner or family move-in, substantial renovation and removing the unit from the market. Tenants displaced by renovation, removal or move-in have a five-year right to return. A notice missing any required element is invalid. See our just cause eviction guide.

Union City rental property rules

Registration. Both Chapter 5.50 and Chapter 5.55 require landlords to register rental units or properties with the city and pay a cost-recovery fee. Missing registration undermines any eviction.

Business tax. Under Chapter 5.04, residential rentals fall in Category 4 at 0.225% of gross receipts, with a $154 minimum and the first $25,000 of receipts exempt. Mobile home parks pay a flat $581 plus $45 per space.

Mobile home parks. Chapter 16.40 limits space rent increases to the lesser of 7% or 90% of the Bay Area CPI change, once every 12 months. Unused increases cannot be banked, and rent does not reset when a home is sold. A narrow exception applies when a dealer removes a home and sells a new one to a new tenant. Owners can petition for more, with 90 days’ notice, before a hearing officer who must be a retired judge.

Building and closing-cost issues

Many Union City complexes are 1970s and 1980s wood-frame garden apartments with tuck-under parking, which warrant a seismic retrofit review. We did not verify a mandatory city soft-story program. Buildings of three or more units with elevated balconies need SB 721 inspections. Union City is not on the County Clerk-Recorder’s list of cities with an added full-value conveyance tax. Its own Chapter 3.08 tax of $0.275 per $500 is administered by the County Recorder, so confirm the total with escrow.

Underwriting a Union City multifamily purchase

1. Confirm every unit is registered and the owner holds a current city business license, or evictions may fail.
2. Check that each rent increase in the past year included the rent review notice. Increases without it are void.
3. Model increases at or under the state cap, and expect review requests above 7%.
4. Ask for any tenant-rights notices, termination notices and right-to-return obligations from past move-outs.
5. Collect leases, the rent roll and two years of statements, and get estoppel certificates.
6. Add the 0.225% gross receipts tax, registration fees and reassessed property tax to your rental property analysis.

Questions people ask

Sources & notes

1. Union City Municipal Code Chapter 18.32, Residential Districts (GoCodebook)
2. Chapter 18.37, SEMU-R, Chapter 18.38, CSMU and Chapter 18.102, DIPSA
3. Chapter 18.31, SB 9
4. Chapter 5.50, Residential Landlord and Tenant Relations
5. Chapter 5.55, Rent Review
6. Chapter 16.40, Mobilehome Rent Review
7. Chapter 5.04, Business Taxes and Chapter 3.08, Documentary Stamp Tax
8. California Attorney General, Rent Caps and Alameda County Clerk-Recorder

Note: Chapter 5.50 does not state relocation amounts or notice periods. Confirm any no-fault eviction plan with counsel.

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

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