Portola Valley · Building on your lot

Lot splits under SB 9 in Portola Valley

Portola Valley's own rules on lot splits under SB 9, with the code text for every value.

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

What Portola Valley's code says

Portola Valley code What Portola Valley's code adds
How the lot may be divided	2 parcels of about equal area; neither may be smaller than 40% of the original lot. Applies: Applies to an SB 9 lot split. § 17.13.040 · code text provided that neither parcel shall be smaller than forty percent of the lot area of the original parcel proposed for subdivision.
Minimum new lot size	No new parcel may be smaller than 1,200 square feet. § 17.13.040 · code text In no instance shall any resulting parcel be smaller than one thousand two hundred square feet in area.
Setbacks	At least 4 feet from side and rear parcel lines. Applies: Applies to any new SB 9 dwelling unit. § 18.27.060 · code text The minimum side and rear setback for any new SB 9 dwelling unit shall be four feet from the side and rear parcel lines. No setback is required. Applies: Applies to a new SB 9 unit built in the same location as an existing structure. § 18.27.060 · code text However, no setback is required for a new SB 9 dwelling unit constructed in the same location as an existing structure on the parcel. At least 4 feet. Applies: Applies to front and side setbacks of newly created parcels. § 17.13.040 · code text Front and side setbacks shall be at least four feet. No setbacks are required. Applies: Applies to an existing structure on the parcel, measured from a proposed property line. § 17.13.040 · code text No setbacks shall be required for an existing structure on the parcel from a proposed property line.
Standards	No more than 2 dwelling units on each new lot, counting existing and new units. Applies: Applies to an SB 9 lot split. § 17.13.040 · code text The subdivision shall create no more than two new parcels of approximately equal area provided that neither parcel shall be smaller than forty percent of the lot area of the original parcel proposed for subdivision. In no instance shall any resulting parcel be smaller than one thousand two hundred square feet in area. At most 16 feet vertical height and 16 feet maximum height. Applies: Applies to an SB 9 unit with setbacks smaller than the base zoning district requires. § 18.27.060 · code text Sixteen feet vertical height and sixteen feet maximum height for a SB 9 unit where the setbacks are less than those of the base zoning district. At most 18 feet vertical height and 24 feet maximum height. Applies: Applies to an SB 9 unit with setbacks that meet the base zoning district. § 18.27.060 · code text Eighteen feet vertical height and twenty-four feet maximum height where the setbacks comply with those of the base zoning district. This includes daylight planes, where applicable. New lot lines must be free of jogs. Applies: SB 9 lot split, unless existing conditions prevent straight lines or straight lines would block lots for 2 units of 800+ square feet. § 17.13.040 · code text Proposed lot lines shall be free of jogs in alignment, except where existing physical conditions and established property lines preclude the establishment of straight property boundaries, or such alignment would prohibit the creation of lots which are capable of being developed with two residential units that are at least 800 square feet each. A 25-foot-wide panhandle or access easement. Applies: Applies to new parcels without direct frontage on a public or private road. § 17.13.040 · code text A twenty-five-foot-wide panhandle (for a flag lot) or an ingress/egress easement shall be provided for all new parcels that do not have direct frontage on a public or private road. Residential and emergency vehicle access that meets Woodside Fire Protection District standards. Applies: Applies to all proposed lots and all new units. § 17.13.040 · code text Proposed lots shall provide residential and emergency vehicle access to or provide access to a public or private street. Such emergency vehicle access shall be in accordance with the Woodside Fire Protection District's standards. New units must connect to public sewer or have a private wastewater system fully inside the parcel. Applies: Applies to all newly created dwelling units. § 18.27.060 · code text All newly created dwelling units shall be connected to public sewer or provide a private wastewater system that is fully contained within the parcel boundaries. Residential uses only. Applies: Applies to units created under the SB 9 rules. § 18.27.060 · code text Land uses of any units created under this chapter are limited to residential uses.
Owner occupancy	At least 3 years. Applies: The applicant signs an affidavit to live in 1 unit as principal residence. § 17.13.040 · code text The applicant for an SB 9 lot split shall sign an affidavit stating that the applicant intends to occupy one of the housing units as their principal residence for a minimum of three years from the date of the approval of the urban lot split. Does not apply. Applies: Applies when the applicant is a community land trust or a qualified nonprofit corporation under state tax law. § 17.13.040 · code text This requirement shall not apply if the applicant is a community land trust or a qualified nonprofit corporation as provided in Sections 402.1 and 214.15 of the Revenue and Taxation Code.
Parking	1 off-street parking space. Applies: Applies to each SB 9 unit. § 18.27.060 · code text One off-street parking space is required for each SB 9 unit No parking is required. Applies: Applies when a car share vehicle is within 1 block of the parcel. § 18.27.060 · code text There is a car share vehicle located 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 Portola Valley?

Portola Valley's code: No new parcel may be smaller than 1,200 square feet. (§ 17.13.040); At least 3 years. (The applicant signs an affidavit to live in 1 unit as principal residence.) (§ 17.13.040).

General information, not legal advice.

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