The issuance of a preliminary Flood Insurance Rate Map (FIRM) does not impact flood insurance rates. When FEMA releases a preliminary FIRM and Flood Insurance Study (FIS) report for a community, caution must be exercised in using this data. For insurance purposes, preliminary FIRMs and FIS reports cannot be used to make official flood determinations. The currently effective FIRM is the only official document for this purpose.
However, for regulatory purposes, preliminary FIRMs and FIS reports may be used by the community. Local regulations usually allow for the use of the best available data, and in most instances, the data provided on the preliminary FIRMs is much better than the older data on the currently effective FIRMs. The use of preliminary maps as "best available data" is only allowable when the preliminary data are more conservative than the effective data; i.e. the elevations of the base (1-%-annual-chance) flood are higher or the Special Flood Hazard Area (SFHA) is more extensive. Please contact your community's floodplain administrator to determine whether preliminary data is being used by your community and whether it has any impact on construction or other use of your property.