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Millbrae · Building on your lot

Lot splits under SB 9 in Millbrae

Millbrae's own rules on lot splits under sb 9, with the code text for every value, and the state law underneath.

Each rule below links to the section of the Millbrae Municipal Code it was read from, with the code text one click away (checked October 2026). General information, not legal advice.

What Millbrae's code says

Millbrae code What Millbrae's code adds
How the lot may be divided
  • Neither parcel may be smaller than 40% of the original lot area.
    Applies: Urban lot split.
    § 10.05.3535 · code text
    The urban lot split will create no more than two new parcels of approximately equal area; provided, that one parcel may not be smaller than forty percent of the lot area of the original parcel proposed for subdivision.
Unit size
  • Each unit may be no larger than 800 square feet.
    Applies: SB 9 projects that do not meet the zone's development standards.
    § 10.05.3550 · code text
    For an SB 9 project that does not meet the underlying zoning district development standards, the unit size for each unit shall not exceed eight hundred square feet.
  • Standards are relaxed only enough to allow 2 units of 800 square feet each on each parcel.
    Applies: SB 9 two-unit development or urban lot split.
    § 10.05.3560 · code text
    Any modifications of development standards shall be the minimum modification necessary to avoid physically precluding two units of eight hundred square feet each on each parcel.
Minimum new lot size
  • Each new parcel must be at least 1,200 square feet.
    § 10.05.3535 · code text
    In no instance may any resulting parcel created by the urban lot split be smaller than one thousand two hundred square feet in area.
Setbacks
  • 20 feet.
    Applies: Front setback.
    § 10.05.3550 · code text
    Front: twenty feet.
  • At least 4 feet.
    Applies: Interior and street side setbacks; not for a unit built in the same place and size as an existing legal home.
    § 10.05.3550 · code text
    Interior and street side: minimum four-foot setback. This section does not apply to a SB 9 dwelling unit constructed in the same location and to the same dimensions as an existing legal dwelling.
  • At least 4 feet.
    Applies: Rear setback; not for a unit built in the same place and size as an existing legal home.
    § 10.05.3550 · code text
    Rear: minimum four-foot setback. This section does not apply to a SB 9 dwelling unit constructed in the same location and to the same dimensions as an existing legal dwelling.
Standards
  • SB 9 units must meet the height limit of the underlying zone.
    Applies: Maximum building height.
    § 10.05.3550 · code text
    SB 9 dwelling units must meet the height requirement of the underlying zoning district.
  • The urban lot split may create no more than 2 new parcels of about equal area.
    Applies: Urban lot split parcel layout.
    § 10.05.3535 · code text
    The urban lot split will create no more than two new parcels of approximately equal area; provided, that one parcel may not be smaller than forty percent of the lot area of the original parcel proposed for subdivision.
  • At least 25 feet of frontage along the public street.
    Applies: Lots created by an urban lot split that front on a public street.
    § 10.05.3535 · code text
    A lot created through an urban lot split that fronts on a public street must provide at least a twenty-five-foot lot frontage along a public street.
  • No more than 2 primary dwelling units on any lot created by an urban lot split.
    Applies: Lots created by an urban lot split.
    § 10.05.3535 · code text
    No more than two primary dwelling units may be located on any lot created by an urban lot split.
  • At least 60% of the front yard must be landscaped.
    Applies: Front yard landscaping.
    § 10.05.3550 · code text
    Not less than sixty percent of the front yard shall be landscaped.
  • Paved accessway at least 10 feet wide.
    Applies: Access for 1 to 2 SB 9 units.
    § 10.05.3550 · code text
    Minimum width of paved accessway: ten feet.
  • Paved accessway at most 12 feet wide, or up to the garage door width.
    Applies: Access for 1 to 2 SB 9 units.
    § 10.05.3550 · code text
    Maximum width of paved accessway: twelve feet, or a maximum up to the width of the garage door associated with the driveway.
  • Paved accessway exactly 20 feet wide.
    Applies: Access for 3 to 4 SB 9 units.
    § 10.05.3550 · code text
    Minimum and maximum width of paved accessway: twenty feet.
  • Paved accessway at least 20 feet deep from the city street.
    Applies: Access for 1 to 2 SB 9 units.
    § 10.05.3550 · code text
    Minimum depth of paved accessway from city street: twenty feet.
  • Paved accessway at least 20 feet deep from the city street.
    Applies: Access for 3 to 4 SB 9 units.
    § 10.05.3550 · code text
    Minimum depth of paved accessway from city street: twenty feet.
  • No structures within 3 feet of the accessway.
    Applies: Access for 1 to 2 SB 9 units.
    § 10.05.3550 · code text
    No structures allowed within three feet of accessway.
  • No structures within 5 feet of the accessway.
    Applies: Access for 3 to 4 SB 9 units.
    § 10.05.3550 · code text
    No structures allowed within five feet.
  • At least 3 feet wide.
    Applies: Landscaped strip between every accessway and the side property lines.
    § 10.05.3550 · code text
    All accessways must provide a landscaped strip measuring at least three feet in width between the driveway and side property lines.
Parking
  • 1 garage parking space per unit.
    § 10.05.3550 · code text
    Any SB 9 dwelling unit constructed will provide one garage parking space per unit, except that no parking may be required where:
  • No parking may be required.
    Applies: Parcel within a half-mile walk of a stop in a high-quality transit corridor or a major transit stop.
    § 10.05.3550 · code text
    The parcel is located within one-half mile walking distance of either a stop located in a high-quality transit corridor, as defined in Public Resources Code Section 21155(b), or a major transit stop, as defined in Public Resources Code Section 21064.3;
  • No parking may be required.
    Applies: A designated parking area for 1 or more car-share vehicles is within 1 block of the parcel.
    § 10.05.3550 · code text
    There is a designated parking area for one or more car-share vehicles within one block of the parcel.

Who this affects

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Frequently asked questions

Can I split my lot under SB 9 in Millbrae?

Millbrae's code: Neither parcel may be smaller than 40% of the original lot area. (Urban lot split.) (§ 10.05.3535); Each unit may be no larger than 800 square feet. (SB 9 projects that do not meet the zone's development standards.) (§ 10.05.3550).

General information, not legal advice.

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