Flood Zone AO

What Zone AO means

FEMA assigns Zone AO to areas subject to inundation by 1-percent-annual-chance shallow flooding — usually sheet flow on sloping terrain — where average depths are between one and three feet. Instead of base flood elevations, average flood depths derived from detailed analyses are shown on the Flood Insurance Rate Map.

Zone AO is inside the Special Flood Hazard Area (SFHA). Areas of alluvial fan flooding are also mapped as Zone AO.

The federal mandatory purchase rule

Because Zone AO is inside the Special Flood Hazard Area, the federal mandatory purchase requirement applies: under the Flood Disaster Protection Act of 1973, as amended, a building in this zone that secures a loan from a federally regulated or insured lender in an NFIP-participating community must carry flood insurance for the life of the loan. NFIP building coverage for a residential structure is capped by statute at $250,000, with contents coverage capped at $100,000.

Zones and premiums

Under the NFIP's current pricing methodology (Risk Rating 2.0), a property's flood zone is no longer the primary variable used to set its premium; zones continue to determine whether the mandatory purchase requirement applies. This page describes zone mechanics only and carries no premium statistics.

Verifying a property's zone

Zone boundaries are set by FEMA's flood maps and can change as maps are revised. The authoritative record for any address is FEMA's Flood Map Service Center. For the NFIP policy and claims statistics of a specific ZIP code, use the ZIP lookup tool on this site.