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Key Definitions


An official map of a community, on which the Federal Emergency Management Agency has delineated both the areas of special flood hazards and the risk premium zones applicable to the community.


The land in the floodplain within a community subject to a one percent or greater chance of flooding in any given year. A SFHA is the same as an A-Zone. See what the flood zones mean for you.


The area inundated by the 1% chance flood constitutes the 100-year floodplain of a river, creek, ditch, lake or other source of flooding. This floodplain is also referred to as the Special Flood Hazard Area (SFHA). It is the area of a community where development must be regulated through a local ordinance conforming to the standards of the NFIP.


For purposes of the NFIP, development means any man-made change to improved or unimproved real estate, including, but not limited to, buildings or other structures, filling, mining, dredging, grading, paving, excavation or drilling operations, or storage or equipment/materials.


Zones on the Flood Insurance Rate Map (FIRM) in which the risk premium insurance rates have been established by a Flood Insurance Study.


A-Zones are found on all Flood Insurance Rate Maps (FIRMs). An A-Zone is an area that would be flooded by the Base Flood, and is synonymous with SFHA or a 100-year floodplain. These areas may be numbered as A1 to A30, or as A99, or more commonly they may be unnumbered as A, AE, AH or AO Zones. Numbered A-Zones indicate an area’s at risk to flooding. The key thing to know is the letter A: It means the area is a Special Flood Hazard Area of some type and is subject to regulation.


An X Zone is an area outside of the Special Flood Hazard Area, and reflects the 500-year floodplain. There are two types of Zone X, one is shaded on a map, the other is unshaded. The key thing to know is that these areas are not subject to regulation. However, though they are areas of minimal to moderate risk of flooding, FEMA data shows that up to 30% of all claims come from these areas.


The river channel plus any adjacent floodplain areas that are needed to carry the waters of the base flood without substantial increases in the flood height. NFIP regulations limit this increase to a maximum of one foot, also known as a surcharge. Most communities allow no development in these areas.


The Base Flood is referred to as the 100-year flood and is a measure of flood magnitude based on probability. The Base Flood has a one percent chance of occurring or being equaled or exceeded in any given year.


The height, measured in feet, of floodwater reached during the Base Flood is referred to as the Base Flood Elevation or 100-year flood elevation.


The elevation of the lowest enclosed area (including basement). An unfinished or flood resistant enclosure, usable solely for parking of vehicles, building access or storage in an area other than a basement area, which is not considered a building’s lowest floor, provided that such enclosure is not built so as to render the structure in violation of the applicable non-elevation design requirements of 60.3 of the NFIP regulations.

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