The NFIP requires that a damaged structure to meet the same construction requirements as a new building if the cost of reconstruction, rehabilitation, addition, or other improvements to a building equals or exceeds 50% of the building's market value. Any new construction or substantial improvement must meet the requirements of §205-158. Substantial improvement is defined as "any reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds 50% of the market value of the structure before "start of construction" of the improvement."
For residential properties, this means that the lowest floor (including the basement) must be elevated one foot above the base flood elevation. For nonresidential properties, this means that the lowest floor (including the basement) must be elevated one foot above the base flood elevation or it shall be flood-proofed so that the structure is watertight with walls substantially impermeable to the passage of water and has structural components that have the capacity of resisting hydrostatic and hydrodynamic loads and the effect of buoyancy. Additionally, §205-161B-C provides that residential and nonresidential uses located in the floodway cannot be reconstructed if the reconstruction cost exceeds 50% of the market value prior to the damage occurring. These provisions are enforced at the time of application for a Floodplain Development Permit, which is required prior to approval of a building permit.
For additional information on FEMA's requirements, visit the website