FEMA flood zone codes explained: A, AE, AH, AO, V, VE, and X
Every property in a FEMA-mapped community falls in a flood zone, and the two-letter code decides whether flood insurance is required for a federally backed mortgage. Here is what each code on the National Flood Hazard Layer actually means, in plain language.
The one distinction that matters: in or out of the SFHA
FEMA’s maps draw one line that carries legal weight: the boundary of the Special Flood Hazard Area (SFHA) — the area with a 1% or greater chance of flooding in any given year (often called the “100-year floodplain”). Every zone code starting with A or V is inside the SFHA; zone X is outside it. If a property is inside and the mortgage is federally backed (most are), the lender must require flood insurance. Outside, it’s optional.
Zone codes at a glance
| Code | Meaning |
|---|---|
| A | 1% annual chance floodplain, mapped by approximate methods — no Base Flood Elevation published |
| AE | Same floodplain, but from a detailed study with a Base Flood Elevation (replaces old A1–A30) |
| AH | Shallow ponding, typically 1–3 feet deep (low-lying flat areas) |
| AO | Shallow sheet flow on sloping ground, typically 1–3 feet deep |
| AR / A99 | Areas behind a levee system being restored (AR) or still under construction (A99) |
| V / VE | Coastal 1% zone with additional wave hazard — the strictest building standards |
| X (shaded) | 0.2% annual chance area (“500-year”), or shallow/protected 1% areas — moderate, no mandate |
| X (unshaded) | Outside both the 1% and 0.2% floodplains — minimal mapped flood hazard |
What being in an A or V zone means in practice
- Insurance: mandatory for federally backed loans, via the National Flood Insurance Program or a private carrier. Cost depends on elevation relative to the Base Flood Elevation, construction, and coverage — this is where an elevation certificate can pay for itself.
- Building and remodeling: new construction and substantial improvements must meet floodplain rules (elevating the lowest floor above the BFE, flood vents, and in V zones, engineered foundations).
- Disclosure: in California, whether a property sits in a FEMA SFHA is one of the six statutory items on the Natural Hazard Disclosure statement every seller must provide.
Common misconceptions
- “It hasn’t flooded here in decades, so the map is wrong.” The zones describe an annual probability, not a schedule. Long quiet stretches are expected — and say nothing about next winter.
- “Zone X means no flooding is possible.” It means no mapped 1%-or-greater hazard. Local drainage, atmospheric-river storms, and creek overflows outside the mapped floodplain still cause claims every year.
- “The map never changes.” FEMA revises maps as studies complete, and owners can seek a Letter of Map Amendment (LOMA) if their structure is naturally above the flood elevation — which can lift the insurance mandate.
Bay Area context
Around San Francisco Bay, the mapped 1% zones concentrate along the bay margins and creek corridors — much of Alameda, Foster City, the North Bay river valleys along the Napa and Russian Rivers, and low-lying stretches of San Jose along Coyote Creek and the Guadalupe River. Our city pages show what share of each city’s area falls inside a mapped FEMA zone.