Multifamily and Duplex Properties for Sale in Millbrae: Zoning and Rent Rules

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What multifamily in Millbrae looks like

Millbrae’s income property includes duplexes and triplexes in its R-2 neighborhoods, small and mid-size apartment buildings in R-3 areas near El Camino Real, and newer transit-oriented buildings around Millbrae Station, served by BART and Caltrain. Homes with ADUs round out the market. The airport next door affects nearly every property through noise and disclosure rules. For two to four units, see financing 2-4 unit properties; for five or more, apartment building loans.

Where the zoning allows it

Millbrae’s zoning chapter, Chapter 10.05, sets the residential districts below. The specific plan districts follow their own plan documents.

District	Units	Key standards
R-2 Duplex/Triplex (Art. VII)	Duplexes and triplexes	2,500 sq ft of lot per unit; 7,500 sq ft lots for triplexes. 50% coverage. FAR 88%. 30 ft with a qualifying sloped roof, otherwise 25 ft
R-3 Multifamily (Art. VIII)	Multifamily of four or more units	1,000 sq ft of lot per unit; 5,000 sq ft interior lots. 75% coverage. No FAR limit. 40 ft
C Commercial (Art. X)	Residential flats by conditional use permit	40 ft; no FAR limit
DTECRSP (Art. XI)	Downtown mixed use	Standards set by the 2022 Downtown and El Camino Real Specific Plan
MSAPD (Art. XVII)	Station-area housing and mixed use	Standards set by the Millbrae Station Area Specific Plan
R-1 and R-1LL	One home per lot, plus ADUs and SB 9 where eligible	R-1: 5,000 sq ft per unit, FAR 55%. R-1LL: 10,000 sq ft per unit

R-2 details. Interior lots must be at least 50 feet wide and corner lots 60 feet. The R-2 FAR counts lofts, attics, covered decks and porches under defined rules. The Planning Commission can grant exceptions on very steep lots or lots burdened by large easements.

Specific plans. In December 2022 the city approved its 2040 General Plan and Downtown and El Camino Real Specific Plan, which supports mixed-use development near the station, along with zoning amendments. The station area plan update began in 2014; its Notice of Preparation studied about 1,750 homes across 116 acres. That figure was an assumption studied in 2014, not a current entitlement count.

Density bonus. Projects of five or more units may use state density bonus law, which the zoning chapter incorporates.

ADUs and SB 9. State ADU law and SB 9 apply to qualifying lots; we did not review Millbrae’s ADU provisions. 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, puts San Mateo County in the San Francisco area. Covered units may rise up to 8.8% for increases from August 1, 2026 through July 31, 2027. Millbrae does not appear on the AG’s list of cities with local apartment rent ordinances, and we found no local relocation or registration ordinance. AB 1482’s just-cause rules apply to covered tenancies. See our AB 1482 guide and just cause eviction guide.

Millbrae rental property rules

SFO compatibility. Article XVI of Chapter 10.05 ties new development to the San Francisco International Airport land use compatibility plan. The chapter writes that requirement into the R-1, R-2, R-3, C, DTECRSP and station area districts. Depending on location, a project may need:

an airport real estate disclosure notice to buyers or tenants
noise evaluation and sound insulation
an avigation easement
safety and airspace review

For an investor, that means checking whether existing units were built with insulation or easements, and planning for those steps when adding units.

Transfer tax. The County’s documentary transfer tax is 55 cents per $500. The County names only the City of San Mateo as adding a city tax, and we found no Millbrae transfer tax; confirm with escrow.

Short-term rentals. We did not verify Millbrae’s short-term rental rules; confirm with the city before underwriting short stays.

Airport noise, older buildings and parking

Airport noise is the defining building issue in Millbrae. Ask for any acoustical reports and confirm window and ventilation upgrades in units under the flight paths. Older wood-frame apartment buildings with parking under the units warrant a seismic retrofit review, and buildings of three or more units with elevated balconies need SB 721 inspections. In the R-1 districts, carports built before October 13, 2009 are treated differently for required parking. If you plan to add an ADU or SB 9 unit behind a home, confirm how the city counts that parking.

Underwriting a Millbrae multifamily purchase

Confirm the district; three units are the R-2 maximum, and R-3 begins at four.
Check the lot area per unit: 2,500 sq ft in R-2 and 1,000 sq ft in R-3.
Classify units under AB 1482 and model covered increases at or below 8.8%.
Review airport disclosures, noise mitigation and any avigation easement on title.
Collect leases, the rent roll and estoppel certificates.
Rebuild expenses with reassessed taxes and insurance in our rental property analysis.

Questions people ask

How many units can I build in Millbrae’s R-2 zone?

Up to three, as a duplex or triplex, at one unit per 2,500 square feet of lot. A triplex needs a 7,500-square-foot lot.

How dense can R-3 apartments be?

One unit per 1,000 square feet of lot, up to 40 feet tall, with 75% coverage and no FAR limit.

Is there rent control in Millbrae?

No local rent ordinance. AB 1482 applies to covered units.

What does the airport require?

Depending on location, disclosure notices, noise evaluation and mitigation, avigation easements and safety and airspace review under the SFO compatibility plan.

Where is new high-density housing planned?

Around Millbrae Station under the station area plan, and downtown under the 2022 Downtown and El Camino Real Specific Plan.

Can I add apartments over a shop?

In the C district, by conditional use permit.

Sources & notes

Note: We did not review the specific plan documents, the Housing Element, ADU or short-term rental rules, or SFO noise contour maps.

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

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