The National Flood Insurance Program (NFIP) requires that if the cost of repair, reconstruction, rehabilitation, addition or other improvements to a building equals or exceeds 50% of the building's assessed value within a three year period, then the entire building must meet the current flood standards as a new building.

Substantially damaged buildings must also be brought up to current flood standards (i.e. a residence is substantially damaged if the cost of repairs equals or exceeds 50% of the building's depreciated value of improvements before it was damaged).  The value of improvements are cumulative over a three year period.