What is the 50% rule?

The flood maps for Key West first became effective December 31, 1974. Buildings constructed after that date were required to be at certain 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 it’s market value. Once that threshold is reached, renovation plans must include elevating the home to current flood levels.


Actually, the first flood maps were effective circa 1970/71, back when the NFIP was administered by the U.S. Department of Housing and Urban Development (HUD) . When Federal Emergency Management Agency (FEMA) took over, it had great difficulty discerning records for the early years of the program. As a result, FEMA stipulated, that any community with flood maps having an effective date prior to December 21, 1974 - such as Key West - would now be governed by this 1974 date rather than the earlier map dates.

Show All Answers

1. What is the 50% rule?
2. What's a "regulated flood zone?"
3. How is the market value of my building determined in connection with the 50% rule?
4. I believe my house is worth more than the Adjusted Property Appraiser's value, so my 50% threshold should be higher. How do I validate this?
5. How is the value of improvements determined?
6. Instead of elevating my home, can I dry floodproof it?
7. Does the 5-year rule reset with a change of ownership?
8. Instead of elevating my commercial building, may I dry floodproof it?
9. How high does my building need to be elevated?
10. My lot is above sea level, so how high on the lot must I raise my house?
11. An Elevation Certificate shows my first floor is only 1/4 inches below the required elevation. Isn't that close enough?
12. Do I need to elevate my building if I plan to substantially renovate it, but the elevation certificate shows that it's higher than the flood level, but lower than the building code requirement?
13. My building has been officially designated a Historically Contributing Structure. Am I still required to elevate it?
14. What are some examples of the ways in which structures can be substantially improved?
15. What is a Substantially Damaged Structure?
16. What the difference between Substantial Improvement and Substantial Damage?
17. In terms of the National Flood Insurance Program regulations, if a structure is determined to be substantially damaged, what must happen to that structure?
18. There are multiple buildings on one lot, that I want to build/renovate. Why am I being asked to file a building permit application for each one separately?
19. Do I need to elevate my building if I recently renovated my building to 49% of its market value, then a fire damaged a room and it's going to cost 1% of the value for repairs?
20. Does the building need to be elevated because a hurricane damaged the roof costing 10% value to repair after I renovated my home to 42%?
21. I have a shed (or garage) in the back yard, that I want to convert to a bedroom (or other living space). Does it have to be elevated?
22. The second floor of my building is well above the flood level. Are repairs to this portion of the building included in the Substantial Improvement calculations?
23. How high does a mobile home need to be elevated?
24. If a building's construction was permitted before the flood map date, but finished after that date, what rules apply?
25. Does solar equipment count toward the 50%?
26. Does only an addition need to be elevated, or the entire building?