Multifamily and Duplex Properties for Sale in San Mateo: Zoning and Rent Rules

What multifamily in San Mateo looks like

The City of San Mateo has one of the Peninsula’s larger stocks of older apartment buildings: duplexes and small walk-ups in the R2 and R3 neighborhoods on both sides of El Camino Real, larger mid-century complexes in R4 and R5, downtown buildings with apartments over shops, and newer transit-oriented projects at Bay Meadows and near the Hillsdale station. Two local rules shape every purchase: a tenant protection ordinance that took effect December 31, 2025, and a city transfer tax charged on top of the County’s. For two to four units, read financing 2-4 unit properties; for larger buildings, see apartment building loans.

Where the zoning allows it

Title 27 sets density by minimum parcel area per dwelling unit, which shrinks as lots get larger.

Older small lots. Parcels northeast of El Camino Real recorded before March 3, 1947 may use smaller 4,000-square-foot, 40-foot-wide lot standards at 2,200 square feet per unit, which can matter in older neighborhoods east of El Camino.

Supportive housing. Supportive housing is a use by right in R3 under state law, subject only to the objective standards for other multifamily projects.

SB 9. Chapter 27.21, adopted by Ordinance 2022-10, implements SB 9 in single-family areas. It allows up to four units with no more than two primary homes, bars rentals under 30 days, and prevents separate sale of two primary units until an urban lot split map records. See our SB 9 lot split guide and ADU investment guide; ADUs and JADUs are in Chapter 27.19.

Rent rules: state rent cap plus local just cause and relocation

Rent cap. The Attorney General’s rent cap page, updated July 16, 2026, places San Mateo County in the San Francisco Area, with covered units allowed up to 8.8% for increases from August 1, 2026 through July 31, 2027, and names East Palo Alto as the county’s only city with local rent stabilization. The City of San Mateo has no local rent cap.

Residential Tenant Protection Program. Ordinance 2025-11, adopted 5-0 on December 1, 2025 and effective December 31, 2025, added Chapter 10.100. It builds on Civil Code Section 1946.2 rather than replacing its coverage, and it sunsets January 1, 2030 unless extended.

• Just cause at 11 months. Just cause protection starts after 11 months of lawful occupancy instead of the state’s 12.
• Relocation. For any no-fault termination, regardless of income, the owner pays one month’s rent. Half is due within 15 days of the notice, and the rest is a final-month waiver or cash by move-out. The payment is credited against state relocation.
• Strict compliance. A notice that does not strictly comply is void.
• Cure notice. Curable lease violations need a notice and chance to cure first.
• Tenant notice. Landlords must give tenants an English and Spanish notice of rights; existing tenants were due theirs by February 1, 2026.
• After a remodel or demolition. Former tenants must be told when the unit is available again.
• Retaliation. Raising rent or cutting services because a tenant used the chapter is barred.

See our AB 1482 guide and just cause eviction guide.

San Mateo rental property rules

• Short-term rentals. Under Chapter 5.66, any dwelling except an ADU can be registered, unhosted stays are capped at 120 days a year, occupancy is two per bedroom or ten per property, and registration ends on sale.
• City transfer tax. Section 3.48.010, amended by Ordinance 2022-15, charges 0.5% of the price under $10 million and 1.5% at $10 million or more, in addition to the County’s documentary transfer tax of $0.55 per $500. At $10 million or more, the higher city rate applies to the full price.

Older buildings, seismic and balconies

Many older San Mateo apartment buildings are wood frame, some over open tuck-under parking. Have such buildings reviewed for seismic retrofit needs, and budget SB 721 balcony inspections for buildings of three or more units with elevated balconies or walkways. If a renovation will require tenants to leave, remember the relocation and notice rules above.

Underwriting a San Mateo multifamily purchase

1. Add the city transfer tax to closing costs, and check whether the price crosses $10 million.
2. Classify units under AB 1482 and model increases at or below 8.8% for covered units.
3. Budget one month’s rent per unit for any planned no-fault termination, and confirm tenant rights notices were given.
4. Check unit count against the lot-area-per-unit table; extra units may be legal nonconforming.
5. Collect leases, the rent roll and estoppel certificates.
6. Rebuild expenses with reassessed taxes, SB 721 and seismic costs in our rental property analysis.

Questions people ask

Sources & notes

1. City of San Mateo Law Library, Title 27 Zoning
2. Sections 27.22.040, 27.24.040 and 27.26.050, R3 to R5 standards
3. Chapter 27.21, SB 9 overlay
4. Chapter 10.100, Residential Tenant Protection Program
5. Ordinance 2025-11
6. Chapter 5.66, Short-Term Rentals
7. Section 3.48.010, Real Property Transfer Tax
8. San Mateo County Clerk-Recorder, documentary transfer tax
9. California Attorney General, rent caps

Note: We read the code through the city’s law library and its published HTML download. We did not review Chapter 27.19 (ADUs), the downtown residential and mixed-use overlay chapters, the TOD, Hillsdale or Bay Meadows plan standards, or the city’s affordable housing resolution. The age of the apartment stock is a general observation, not from a source.

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

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