What is a 500-year floodplain?
A 500-year floodplain is land with a 0.2% chance of flooding in any year. FEMA maps it as shaded zone X (zone B on older maps).
In more detail
It is the band of moderate risk just outside the 100-year floodplain. Lenders don't require flood insurance here, but floods in this band are not rare: about a 6% chance over 30 years.
Hospitals, emergency facilities and other critical buildings are often held to the 500-year line, which is a hint at how seriously planners take it.
What it means when you buy
A building in the 500-year floodplain usually has lower insurance costs and no lender mandate. Price a policy anyway for low-lying buildings, and check how close the 100-year line runs.
How the free flood check shows it
The free flood check shows both lines, so you can see whether a building is in the moderate band or sitting at the edge of the high-risk zone.
Check the flood zone for an address, free
Enter any US address to see its FEMA flood zone and a map of the flood areas around it. Add your email to see which buildings sit in the flood zone and the risk numbers.