Flood Zone A vs AE: Key Differences

Flood Zone A is a high-risk area within the Special Flood Hazard Area (SFHA) where FEMA has determined there is a 1% annual chance of flooding (the "100-year flood"). However, Zone A is based on an approximate study, meaning FEMA has identified the area as flood-prone but has not conducted the detailed hydraulic analysis needed to establish a Base Flood Elevation (BFE).

Without a BFE, Zone A communities face additional challenges. Local officials must use the best available data to estimate flood levels when issuing building permits. Property owners seeking a LOMA may find the process more complex because there is no published BFE to compare their elevation against.

Zone A designations are most common in rural or less-developed areas where FEMA has not yet allocated resources for a detailed flood study. Over time, many Zone A areas are reclassified to Zone AE as FEMA completes new studies.

Flood Zone AE is also a high-risk SFHA with the same 1% annual chance of flooding, but it is backed by a detailed hydrologic and hydraulic engineering study. This study establishes a precise BFE for the area, which is the elevation that floodwaters are expected to reach during the base flood event.

The BFE is shown on the Flood Insurance Rate Map (FIRM) and serves as the regulatory benchmark for building construction, insurance rating, and floodplain management. Note that BFEs on the FIRM are rounded to the nearest foot. For more precise values, refer to the flood profiles in the Flood Insurance Study (FIS).

Zone AE is the most common high-risk designation in the United States. If your property is in Zone AE, you have access to more precise data about your flood risk, clearer building requirements, and a more straightforward path to a LOMA if your elevation is at or above the BFE.

Both Zone A and Zone AE require flood insurance for properties with federally regulated or government-backed mortgages. However, the availability of BFE data in Zone AE can influence how premiums are calculated.

Under Risk Rating 2.0, FEMA uses multiple factors to price flood insurance, including distance to water, flood frequency, building characteristics, and elevation. In Zone AE, the known BFE allows for a more precise comparison with your property's actual elevation, which can work in your favor if your structure is well above the BFE.

In Zone A, the absence of a BFE means FEMA relies on other available data to assess risk. An Elevation Certificate can still help demonstrate your property's elevation, but without a published BFE for comparison, the rating may be less favorable.

Both zones require new construction and substantial improvements to be elevated above the base flood level. The difference is how that level is determined.

If you believe your property is incorrectly mapped in either zone, you can dispute the designation through FEMA's Letter of Map Change process.

On older FIRM panels published before 1986, you may see zones labeled A1 through A30 instead of AE. These numbered zones are functionally the same as Zone AE. Each number corresponded to a specific flood insurance rate, but this system was replaced when FEMA adopted the letter-based designation.

If your FIRM still shows a numbered A zone, the property is treated the same as Zone AE for insurance and building purposes. When FEMA updates the map, these numbered zones are converted to Zone AE with published BFE values.