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Marin County · Building on your lot

Building in a flood zone in Marin County

Marin County's own rules on building in a flood zone, with the code text for every value.

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

What Marin County's code says

Marin County code What Marin County's code adds
Floodplain permit
  • Permit applications for construction, substantial improvements, grading, paving, mining, drilling or manufactured homes are reviewed for flood-prone areas.
    § 23.09.033 · code text
    All permit applications for proposed construction, substantial improvements or other development including but not limited to buildings or other structures, mining, dredging, paving, grading, excavation, drilling and placement of manufactured homes shall be reviewed by the department of public works to determine whether such construction or other development is proposed within flood prone areas and therefore subject to the provisions of this chapter.
Building in a floodway
  • No fill, construction or other encroachment unless a registered civil engineer certifies it will not raise base flood levels.
    Applies: Applies in designated floodways.
    § 23.09.038 · code text
    Prohibit encroachments, including fill, new construction, substantial improvements and other development, unless certification by a registered civil engineer is provided demonstrating that encroachments shall not result in any increase in flood levels during the occurrence of the base flood discharge.
Height of the lowest floor
  • The lowest floor, including basement, must be at or above the base flood elevation.
    Applies: New or substantially improved buildings in special flood hazard areas.
    § 23.09.034 · code text
    New construction and substantial improvement of any structure shall have the lowest floor, including basement, elevated to or above the base flood elevation.
  • Lowest floor: above highest adjacent ground, at least the flood map depth number, or at least 2 feet if none.
    Applies: New or substantially improved buildings in Zone AG or VO.
    § 23.09.034 · code text
    New construction and substantial improvement of any structure in Zone AG or VO shall have the lowest floor, including basement, elevated above the highest adjacent grade and at least as high as the depth number specified in feet on the FIRM or at least two feet if no depth number is specified.

Who this affects

HomeownersContractorsDesigners

Frequently asked questions

What are the rules for building in a Marin County flood zone?

Marin County's code: Permit applications for construction, substantial improvements, grading, paving, mining, drilling or manufactured homes are reviewed for flood-prone areas. (§ 23.09.033); The lowest floor, including basement, must be at or above the base flood elevation. (New or substantially improved buildings in special flood hazard areas.) (§ 23.09.034).

General information, not legal advice.

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Ask GoCodebook how Marin County's building in a flood zone rules apply to your situation and get an answer that cites the section.

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Marin County Municipal Code — full text