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

What multifamily in San Bruno looks like

San Bruno’s rental housing is mostly duplexes, triplexes and older garden-style apartment buildings in the R-2, R-3 and R-4 neighborhoods near El Camino Real and the downtown, plus newer mid-rise buildings in the transit corridor districts around the Caltrain station. The Bayhill area adds the potential for several hundred new units on former office and shopping center land under overlay zoning. Because the city sits next to SFO, aircraft noise disclosure is part of every residential sale. For two to four units, read financing 2-4 unit properties; for larger buildings, see apartment building loans.

Where the zoning allows it

Chapter 12.96, amended by Ordinance 1947 on April 9, 2024, sets the residential districts. Density is controlled by minimum lot area per unit.

R-3 and R-4 lots must be at least 5,000 square feet, or 6,000 on a corner, with 60% maximum building coverage. Those per-unit figures work out to roughly 22 and 30 units an acre. In the mixed-use districts, single-family homes, duplexes and mobile home parks are not allowed, so a small duplex there is likely nonconforming.

Ministerial approval. Under Chapter 12.245, adopted September 10, 2024, residential projects with at least 20% very low or low income units that meet objective standards are approved by the community development director with no public hearing. Mixed-use projects also qualify if at least half the floor area is residential. Appeals must be filed within 10 days, and projects needing a variance do not qualify.

ADUs and SB 9. ADUs are permitted in R-2, R-3 and R-4, and Chapter 12.90 governs ADUs and JADUs. SB 9 two-unit projects and lot splits can apply on qualifying R-1 lots under state law; we did not find a San Bruno SB 9 chapter, so confirm the city’s objective standards. See our ADU investment guide and SB 9 lot split guide.

Rent rules: state law only

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. Its chart lists East Palo Alto as the only city in the county with local rent stabilization, and we found no tenant protection chapter in San Bruno’s code. San Bruno apartments therefore follow AB 1482’s cap and just-cause rules for covered units, with the usual exemptions for newer buildings and qualifying individually owned homes. See our AB 1482 guide and just cause eviction guide.

San Bruno rental property rules

• Short-term rentals. Chapter 12.270, adopted by Ordinance 1884 in 2020, allows hosted rentals of up to three bedrooms only in an owner’s sole primary residence, and whole-unit rentals for up to 120 days a year.
• ADUs and STRs. ADUs permitted after September 25, 2020 cannot be short-term rentals, and older ADUs qualify only if the main house is owner-occupied.
• STR permits. Permits expire each December 31, are not transferable, and require building and fire inspections plus paid occupancy and business license taxes.
• Airport noise disclosure. Under Chapter 6.18, sellers of single-family and multifamily dwellings must disclose aircraft overflight noise and the 65 CNEL contour on the local option disclosure form.
• Transfer tax. The County’s documentary transfer tax is $0.55 per $500. San Bruno’s Chapter 3.36 sets a $0.275 city tax under the state enabling law, which typically shares the County rate; confirm in escrow.

Noise insulation, older buildings and seismic

Inside the 65 CNEL contour, a home rebuilt after major damage or renovated at 25% or more of its market value must meet FAA noise insulation standards, and owners may not reduce FAA-funded insulation already installed. That can add cost to a major apartment rehab. San Bruno’s older wood-frame apartments, often over tuck-under parking, merit a seismic retrofit review, and buildings of three or more units with elevated balconies need SB 721 balcony inspections.

Underwriting a San Bruno multifamily purchase

1. Check unit count against the lot area per unit in R-3 or R-4; extra units may be nonconforming.
2. Classify units under AB 1482 and model increases at or below 8.8% for covered units.
3. Do not count on nightly income from a post-2020 ADU.
4. If you plan a major renovation, confirm whether the building is inside the 65 CNEL contour.
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. San Bruno Chapter 12.96, Establishment of Districts (GoCodebook)
2. Chapter 12.280, Mixed-Use Zoning Districts
3. Chapter 12.290, Bayhill Specific Plan Districts
4. Chapter 12.245, Multifamily Housing Ministerial Review
5. Chapter 12.270, Short-Term Residential Rentals
6. Chapter 6.18, Airport noise disclosure
7. Chapter 3.36, Real Property Documentary Stamp Tax
8. San Mateo County Clerk-Recorder, documentary transfer tax
9. California Attorney General, rent caps

Note: We did not review Chapter 12.90 (ADUs), Section 12.200.040 (R-2 standards), the affordable housing and density bonus chapters, or the housing code. Units-per-acre figures are our arithmetic from the code’s lot-area-per-unit rules.

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

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