Mill Valley · Building on your lot

Lot splits under SB 9 in Mill Valley

Mill 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 Mill Valley Municipal Code it was read from, with the code text one click away (checked October 2026). General information, not legal advice.

What Mill Valley's code says

Mill Valley code What Mill Valley's code adds
How the lot may be divided	New lots must be about equal; neither may be smaller than 40% of the original lot area. Applies: Urban lot split. § 21.29.040 · code text Each newly created lot shall be approximately equal in lot area provided that one parcel shall not be smaller than 40% of the lot area of the original parcel proposed for subdivision.
Minimum new lot size	Each new lot must be at least 1,200 square feet. Applies: Each newly created lot. § 21.29.040 · code text In no instance shall a new parcel be less than 1,200 square feet in lot area.
Standards	An urban lot split must create exactly 2 parcels. Applies: Urban lot split parcel map. § 21.29.040 · code text The parcel map to subdivide an existing parcel shall result in two parcels. No more than 2 dwelling units. Applies: Each newly created lot. § 21.29.040 · code text Newly created lots shall include no more than two dwelling units as defined in Government Code Section 66411.7(j)(2). No setback required. Applies: Existing structures. § 21.29.040 · code text No setback shall be required for an existing structure. A 25-foot-wide panhandle or a 16-foot access easement. Applies: New lots without direct frontage on a public or private road. § 21.29.040 · code text A 25-foot-wide panhandle (for a flag lot) or a 16-foot ingress/egress easement shall be provided for all newly created lots that do not have direct frontage on a public or private road. A fire access road at least 20 feet clear width, able to carry 45,000 pounds. Applies: New units more than 150 feet from a city right-of-way, on an urban lot split. § 21.29.040 · code text All new dwelling units located more than 150 feet from a City right-of-way must be accessible through a path of travel that is accessible for emergency service vehicles by way of an approved fire apparatus access road at least 20 feet in clear width with an approved driving surface capable of supporting the imposed load of fire apparatus weighing at least 45,000 pounds. Driveways must be at least 16 feet wide. Applies: Driveways to new buildings on an urban lot split. § 21.29.040 · code text Driveways that provide access to new buildings shall have a minimum width of 16 feet with an approved driving surface capable of supporting the imposed load of a fire apparatus weighing at least 45,000 pounds. Driveway grade 18% or less, cross slope of 8%, inside curve radius at least 27 feet. Applies: Driveways on an urban lot split. § 21.29.040 · code text Driveways shall have grades of 18% or less, cross slope of eight percent, and a horizontal inside radius of curvature no less than 27 feet. Standards are waived if they would block 2 units on either new parcel or force units below state minimum size. Applies: Urban lot split objective standards. § 21.29.040 · code text Notwithstanding the foregoing, the following standards shall be waived if they have the effect of physically precluding the development of two dwelling units on either of the resulting parcels or that would result in dwelling units with less than the minimum allowable square footage permitted by state law.

Who this affects

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Frequently asked questions

Can I split my lot under SB 9 in Mill Valley?

Mill Valley's code: Each new lot must be at least 1,200 square feet. (Each newly created lot.) (§ 21.29.040); An urban lot split must create exactly 2 parcels. (Urban lot split parcel map.) (§ 21.29.040).

General information, not legal advice.

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Mill Valley Municipal Code — full text