FEMA flood zones and Base Flood Elevation (BFE)

One-line orientation

FEMA maps flood risk by zone. The Base Flood Elevation (BFE) is the expected elevation of the 1%-annual-chance flood, and local freeboard may require the lowest floor to be higher.

Key points

• FEMA + FIRMs: the Federal Emergency Management Agency designates flood zones on Flood Insurance Rate Maps (FIRMs), which govern flood risk, insurance, and construction rules.
• Special Flood Hazard Area (SFHA) — high risk / “100-year floodplain”: a 1% or greater annual chance of flooding.
  • Zone A: basic high-risk riverine zone, no detailed BFE data provided.
  • Zone AE: 1%-chance riverine zone with BFEs provided (along rivers/streams) — stricter codes and insurance. (Shallow-flooding variants AO/AH also provide depths/BFEs.)
  • Zone V: coastal high-hazard zone — 1% chance plus storm-induced wave action; bare V has no BFE.
  • Zone VE: coastal high-hazard with wave action and BFEs provided.
• Moderate-to-low risk — “500-year floodplain”: less than 1% annual chance.
  • Zone X (shaded): moderate hazard, between the 100- and 500-year limits (0.2% annual chance).
  • Zone X (unshaded): minimal hazard, outside the 500-year floodplain.
  • (Older terms: B = shaded X, C = unshaded X.)
• Undetermined risk — Zone D: possible but undetermined hazard; no mandatory insurance, but recommended.
• Base Flood Elevation (BFE): the rounded whole-foot elevation the 100-year flood is expected to reach. The NFIP baseline is the building’s first/lowest floor at or above the BFE; freeboard or local code may require it higher.
• Freeboard: an added safety margin above the BFE set by the community, raising the lowest floor higher than the BFE.
• The surveyor’s role: public FEMA maps aren’t detailed at the project scale, so the surveyor establishes the flood boundaries and site elevations on the survey to fix the minimum height above grade.

Confusions / comparison

Zone	Risk	Setting	Wave action	BFE provided?
A	High (1% / 100-yr SFHA)	Riverine	No	No (detailed data not available)
AE	High (1% SFHA)	Riverine	No	Yes
V	High (1% SFHA)	Coastal	Yes	No
VE	High (1% SFHA)	Coastal	Yes	Yes
X (shaded)	Moderate (0.2% / 500-yr)	—	—	—
X (unshaded)	Minimal (outside 500-yr)	—	—	—
D	Undetermined	—	—	—

Related

→ Water table (this module): groundwater vs surface flood risk · Survey (this module): the surveyor sets site flood boundaries and elevations · Code: floodplain construction and elevation requirements in the building code.