Flood · Glossary

FEMA Zone AO

Updated 2026-07-18

FEMA Zone AO is a Special Flood Hazard Area subject to shallow flooding, usually sheet flow, with average depths typically shown on the map. California sites in Zone AO may need finished-floor elevation based on mapped depth plus local freeboard.

What it means

Zone AO generally represents one to three feet of shallow flooding where a conventional base flood elevation is not mapped.

Why it matters for land decisions

Shallow flow can constrain grading, access, drainage, and building elevations.

  • Read the mapped depth.
  • Confirm the local elevation method.

People also ask

Is Zone AO part of the SFHA?

Yes. Zone AO is an A-series Special Flood Hazard Area.

How is elevation set in Zone AO?

Local rules commonly use the highest adjacent grade plus the mapped flood depth and any required freeboard; verify the adopted ordinance.

Official sources

Related terms

FEMA Zone A Special Flood Hazard Area Elevation Certificate

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