Flood Zone Designations: What A, V, X, and AE Mean

High-Risk Flood Zones (Special Flood Hazard Areas)

High-risk flood zones, collectively known as Special Flood Hazard Areas (SFHAs), have at least a 1% chance of flooding in any given year. Properties in these zones with federally backed mortgages are required to carry flood insurance. According to FEMA, approximately 13 million properties are located in SFHAs nationwide.

Zone A

Zone A is the basic high-risk designation for areas with a 1% annual chance of flooding. These areas have been identified as flood-prone but have not had a detailed engineering study to determine base flood elevations. Without BFE data, insurance rates are often set using default assumptions that may overestimate or underestimate actual risk. Many rural counties have large areas mapped as Zone A.

Zone AE

Zone AE is the most common high-risk designation in areas with detailed flood studies. Like Zone A, these areas have a 1% annual chance of flooding, but they include a determined Base Flood Elevation. The BFE is critical for setting insurance rates and building requirements. Properties built above the BFE in Zone AE typically pay lower premiums than those at or below it.

Zone AH

Zone AH designates areas with a 1% annual chance of shallow flooding (typically 1-3 feet), usually in areas of ponding. These zones have determined BFEs and are common in flat terrain where water collects rather than flowing downstream.

Zone AO

Zone AO identifies areas with a 1% annual chance of shallow flooding characterized by sheet flow on sloped terrain. Instead of a BFE, Zone AO maps specify flood depths, typically 1-3 feet. These zones are common in alluvial fans and urban areas with overland flow paths.

Zone V and VE

V zones (Velocity zones) represent the highest-risk coastal areas subject to wave action from storms. Zone V is the basic coastal high-risk designation, while Zone VE includes a determined BFE. Building requirements in V zones are the most stringent, structures must be elevated on pilings or columns, with the lowest floor above the BFE. No fill or permanent enclosures are permitted below the BFE. Insurance premiums in V zones are the highest in the NFIP.

Moderate-Risk Flood Zones

Zone X (Shaded), Zone B

Shaded Zone X (formerly Zone B) represents areas with a 0.2% annual chance of flooding, the 500-year floodplain. While flood insurance is not mandatory in these areas, over 25% of NFIP claims come from moderate and low-risk zones. Preferred Risk Policies offer affordable flood insurance for Zone X properties.

Low-Risk Flood Zones

Zone X (Unshaded), Zone C

Unshaded Zone X (formerly Zone C) represents areas with minimal flood risk, above the 500-year floodplain. These areas have the lowest flood risk but are not risk-free. Changes in upstream development, drainage patterns, and climate can increase flood risk in Zone X areas over time.

Undetermined Risk

Zone D

Zone D is assigned to areas where FEMA has not conducted a flood hazard analysis. No flood risk data is available, and flood insurance rates are based on default assumptions. Zone D areas may have significant flood risk that simply has not been studied.

Why Flood Zones Matter

Your flood zone designation affects your property in several important ways. It determines whether your lender requires flood insurance, influences your insurance premium, dictates building code requirements for new construction and substantial improvements, and affects your property's market value.

Check your county's overall flood risk score on our rankings page and use our county comparison tool to understand how flood zones affect risk across different areas. For more details on reading your flood map, see our guide on how to read FEMA flood maps.