Compares the date construction or substantial improvement to the effective date the initial Flood Insurance Rate Map (FIRM).
• Pre-FIRM: Structures completed or substantially improved prior to the issuance of the community's first FIRM; and
• Post-FIRM: Structures completed or substantially improved after the issuance of the community's first FIRM.

Rates differ based on classification as Pre-FIRM or Post-FIRM structure. Grandfather laws are also affected by Pre or Post-FIRM designations.

Post-FIRM structures MUST comply with the floodplain management requirements and the FIRM in effect at the time of construction. Nothing should be done to the structure to alter it in violation of the subject FIRM.