Establishment of the Design Flood Elevation is covered in R322.1.4. It is defined as the higher of either (1) the base flood elevation, including wave height, that has a 1% or greater chance of flooding in any given year, or, (2) the base flood elevation as established by the locally adopted flood hazard map. In communities that participate in the National Flood Insurance Program, the design flood elevation is typically determined by the Flood Insurance Study, and depicted on the adopted Flood Insurance Rate Map.
In the scenario that you provided, an AE flood zone that is not a Coastal A Zone, the base flood elevation would be 8.0' NGVD for the finished floor elevation as depicted on the adopted map, assuming the garage is constructed in accordance with the exception to R322.2.1. The enclosed garage could be located below 8.0' NGVD as long as the conditions of R322.2.2 are met meaning it is constructed of flood resistant materials, is non-habitable and meets the other criteria found in the Code..
The Florida Building Code, Residential does require a "freeboard" for non-coastal A or AE flood zones of at least 1 foot and up to 3 foot, depending on which area the property falls in. However, a local ordinance may require additional requirements beyond the scope of the Code.
Further guidance for defining the term design flood elevation can be found in ASCE 24-14, Section 1.2, Definitions.
This interpretation was revised on April 24, 2018 to correct an error that was found.
