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

What multifamily in Foster City looks like

Foster City was planned from the start with a large share of attached housing, so its rental stock is weighted toward sizable apartment communities, townhouse and condominium complexes, and a few mixed-use projects, rather than the scattered duplexes found in older Peninsula towns. Small two-to-four-unit buildings are uncommon; for most smaller investors, the entry point is a condo or townhouse unit, or an R-1 home with an ADU or SB 9 unit. For financing, see financing 2-4 unit properties and apartment building loans.

Where the zoning allows it

Foster City’s residential chapters in Title 17 were restated by Ordinance 674 in 2024 and set minimum as well as maximum densities.

Minimum densities. Because R-3 and R-4 set density floors of 15 or 20 units per acre, a redevelopment that rebuilds at lower density may not conform. New multifamily and mixed-use buildings must meet the objective design and development standards in Chapter 17.96. In R-3, ground-level parking no more than four feet above grade does not count as a story.

By-right housing. Under the BRHO, adopted by Ordinance 657 in 2023, the community development director approves qualifying multifamily projects ministerially if 20% of units are restricted for lower-income households. The overlay serves as an alternative to the city’s inclusionary and affordable overlay requirements, can be mapped at an owner’s request, and was written partly with older apartment sites in mind.

ADUs. ADUs are permitted in R-3 under Chapter 17.78. See our ADU investment guide.

SB 9. Foster City’s Chapter 17.79, from Ordinance 683 in 2024, applies only to R-1 and R-1/PD lots outside excluded hazard areas.

• Size. Units are capped at 800 square feet, or 1,200 square feet if lot coverage stays within the base limit.
• Height. No more than two stories and 25 feet, or the main home’s height if lower.
• Setbacks. Side and rear setbacks are four feet.
• Rentals. Units may not be rented for under 30 days.
• Lot splits. The owner signs an affidavit to live in one unit for three years and attests that no affected unit was tenant-occupied in the prior three years.
• Review. Ministerial, with a decision within 60 days.

See our SB 9 lot split guide.

Rent rules: state law only

Foster City has no local rent control ordinance, and the Attorney General’s rent cap page lists East Palo Alto as the only San Mateo County city with one. Updated July 16, 2026, the AG page places San Mateo County in the San Francisco Area. Covered units may rise up to 6.3% for increases from August 1, 2025 and 8.8% from August 1, 2026 through July 31, 2027. Large Foster City apartment complexes built more than 15 years ago are generally covered by both the cap and state just-cause rules, while newer buildings fall under AB 1482’s 15-year rolling exemption. See our AB 1482 guide and just cause eviction guide.

Foster City rental property rules

• No short SB 9 rentals. SB 9 units may not be rented for less than 30 days, and lot splits record a covenant limiting rentals to longer terms.
• Hotel tax. Short stays are subject to the city’s transient occupancy tax under Chapter 3.20; we did not confirm the rate or any separate short-term rental permit.
• Care facilities. R-3 permits community care facilities, transitional and supportive housing and low-barrier navigation centers.
• Transfer tax. The County Recorder’s documentary transfer tax is $1.10 per $1,000. We found no Foster City tax; confirm on the escrow estimate.

Bay fill, lagoons and building age

Foster City was built on filled Bay land around a network of lagoons, so flood zone status, levee protection and soil conditions belong in every inspection. The W Aquatic Development combining district (Chapter 17.40) applies to development along the waterways. Many apartment complexes date from the city’s early decades; check for wood-frame buildings over parking that may warrant a seismic retrofit review, and budget for SB 721 balcony inspections on buildings of three or more units with elevated decks and walkways.

Underwriting a Foster City multifamily purchase

1. Confirm the district and any PD, BRHO or affordable overlay; PD conditions can control use and parking.
2. Identify the building’s certificate of occupancy date to test the AB 1482 15-year exemption, and model covered increases at or below 8.8%.
3. For redevelopment, test the R-3 or R-4 minimum density and the Chapter 17.96 standards.
4. For a condo unit, review HOA rental restrictions, reserves and special assessments.
5. Collect leases and estoppel certificates.
6. Rebuild expenses with reassessed taxes, flood insurance and deck reserves in our rental property analysis.

Questions people ask

Sources & notes

1. Foster City Title 17, Zoning (GoCodebook)
2. Chapter 17.18, R-3 and Chapter 17.20, R-4
3. Chapter 17.28, C-M Commercial Mix
4. Chapter 17.94, By-Right Housing Overlay
5. Chapter 17.79, Two-Unit Developments and Urban Lot Splits
6. Chapter 17.96, Objective Design and Development Standards
7. San Mateo County Assessor-County Clerk-Recorder, documentary transfer tax
8. California Attorney General, rent caps

Note: We did not review the R-T, ADU, affordable housing overlay, senior housing overlay, W district or transient occupancy tax chapters, or the zoning map.

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

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