The lowest floor is the floor of the lowest enclosed area in a building (including a basement), except when the criteria listed in the definition of Enclosed Area below Lowest Floor are met. An unfinished or flood resistant enclosure, usable solely for parking of vehicles, building access or storage in an area other than a basement area is not considered a building's lowest floor; provided, that such enclosure is not built to render the structure in violation of the applicable non-elevation design requirements of Section 60.3 CFR.
The elevation reference point depends on the most restrictive flood zone in which any portion of the building resides. In an A flood zone (any flood zone which starts with the letter A), the lowest floor elevation is calculated as the top of the lowest floor of elevated living area. Non-conditioned/enclosed areas located below the elevated structure which are used exclusively for limited storage, parking, or building access do not count as the “lowest floor”. If a building is located partially or entirely in a V flood zone (coastal high hazard area which has additional hazards due to wind and wave action), the lowest floor elevation reference point is the bottom of the lowest horizontal structural member supporting the elevated lowest floor:
For more information and explanation regarding lowest floor elevation, see also the FEMA “Lowest Floor Guide” at the link below: