The flood maps for Key West first became effective December 31, 1974. Buildings constructed after that date must be at specific minimal elevations above sea level. Existing buildings within regulated flood zones were grandfathered into the National Flood Insurance Program (NFIP) at their current elevations. However, that grandfathered status ceases once the building has been renovated by half its market value. Once that threshold is reached, renovation plans must include elevating the home to current flood levels.