Flood zones A and AE

Zone A

FEMA draws approximate Zone A boundaries from existing information, not from engineering studies.

In Zone A, new subdivisions and developments larger than 50 lots or 5 acres, whichever is less, must include base flood elevation data.

In Florida, local officials may require a permit applicant in approximate Zone A to develop BFE data or use data from another source.

In Florida, if BFE data are not available from another source, local officials may set the BFE at two feet above the highest adjacent grade in some cases.

Sources: Zone A has no BFE; Zone A lines come from existing information; Large subdivisions in Zone A must supply BFE data; Local officials may require a BFE to be developed

Zone AE

Zones AE and the older numbered Zones A1 to A30 are special flood hazard areas where flood water surface elevations have been determined.

Zone AE is the 1 percent annual chance (100-year) floodplain with BFEs. Older maps labeled these areas Zones A1 to A30.

Until a regulatory floodway is designated, new building or fill in Zones A1 to A30 and AE is allowed only if it will not raise the base flood more than one foot.

Sources: Zones AE and A1 to A30 have BFEs; AE replaced the numbered A zones; One foot rise limit before a floodway is set

Zones AH and AO

Zones AO and AH mark shallow flooding: a 1 percent or greater annual chance of flooding to an average depth of 1 to 3 feet, where no clear channel exists.

Zone AH is usually ponding, and its map shows BFEs. Zone AO is usually sheet flow on sloping ground, and its map shows average flood depths instead.

In Zone AO, new and substantially improved homes must have the lowest floor above the highest adjacent grade by at least the depth number on the map, or two feet if none is shown.

Sources: AH and AO are shallow flooding zones; AH is ponding with BFEs; AO is sheet flow with depths; AO zone homes: elevated by the depth number

Building rules in the A zones

New and substantially improved homes in Zones A1 to A30, AE and AH must have the lowest floor, including any basement, elevated to or above the base flood level.

A nonresidential building may either be elevated or be made watertight below the base flood level, with walls substantially impermeable to water.

Where BFE data are used in Zone A, the community must obtain the lowest floor elevation of new and substantially improved buildings and keep a record of it.

Under the minimum criteria, enclosed areas below the lowest floor need at least two flood openings totaling one square inch for every square foot of enclosed area.

A substantial improvement is any rebuild, rehab, addition or other improvement costing 50 percent or more of the building's market value before the work starts.

A building is substantially damaged when restoring it to its condition before the damage would cost 50 percent or more of its market value.

Local officials, usually the floodplain administrator, decide whether a building has been substantially improved or substantially damaged.

Sources: A zone homes: lowest floor at or above BFE; The 50 percent rule for improvements; Local officials make the call

Flood insurance

Regulated lenders may not make, increase, extend or renew a loan secured by a building in a special flood hazard area unless it carries flood insurance for the loan term.

Federal rules require flood insurance purchase in the A zones (A, A1 to A30, AE, A99, AO, AH, AR) and the V zones (V1 to V30, VE, V, VO), among others.

Regulated lenders must accept private flood insurance when its coverage meets the federal requirement.

If a map update puts a building into an SFHA, the NFIP offers a Newly Mapped discount when a policy is bought or renewed within 12 months of the update.

Sources: Lenders must require flood insurance in SFHAs; Zones where purchase is mandatory; Newly mapped discount

Elevation certificates

FEMA describes elevation certificates as an optional NFIP tool for checking a building's First Floor Height and the elevation around it.

A community may require an elevation certificate both before and after construction.

A request to change a flood map finding, such as the flood zone, through a Letter of Map Change must include an elevation certificate.

Before paying for a new one, ask around: former owners may have a copy, and the developer or builder may have been required to get one.

In Florida, the elevation certificate must be completed and sealed by a Florida licensed surveyor, though community officials may complete it for approximate Zone A and Zone AO sites.

In Maricopa County, Arizona, ECs are usually completed by a registered land surveyor or engineer, but a homeowner may complete one in Zones AO and A without a BFE.

Florida permit holders must submit an EC once the lowest floor is placed, before further vertical construction.

Since January 1, 2023, Florida law requires surveyors and mappers to submit a digital copy of every EC they complete to the state Division of Emergency Management.

Sources: Elevation certificates are optional rating tools; Florida: completed and sealed by a Florida licensed surveyor; Homeowners may complete it in AO and A without BFE; Florida surveyors file every EC with the state