Flood.global

Flood zones explained

Every letter on a FEMA flood map stands for a level of risk. Here's what each one means, and what it does and doesn't tell you about your home.

Reviewed October 2026

A swollen river spread over its banks, with trees standing in the water
A river over its banks and into its floodplain in Ulm, Germany. Photo: Bernd Dittrich on Unsplash

What a flood zone is

FEMA's Flood Insurance Rate Maps divide land into zones based on how likely it is to flood. The key line is the 1% annual chance flood, often called the 100-year flood or base flood. It's a flood with a 1-in-100 chance of happening in any given year, not one that happens once a century.

Land that floods in that event is the Special Flood Hazard Area (SFHA). Every zone starting with A or V is inside it. Over a 30-year mortgage, a building in the SFHA has at least a 26% chance of flooding, because a 1% chance every year adds up (1 − 0.99³⁰ ≈ 0.26).

High-risk zones (Special Flood Hazard Area)

Zone What it means
A 1% annual chance of flooding, mapped by approximate methods. No base flood elevation is shown.
AE (and older A1–A30) 1% annual chance of flooding, mapped in detail. The map shows a base flood elevation (BFE), the height floodwater is expected to reach in that flood.
AH Shallow flooding where water ponds, usually 1 to 3 feet deep. A BFE is shown.
AO Shallow flooding where water flows as a sheet down a slope, usually 1 to 3 feet deep. Flood depths are shown instead of a BFE.
AR Areas that were protected by a flood control system, such as a levee, that is now being restored.
A99 Areas that will be protected by a federal flood protection system still under construction.
V Coastal areas with a 1% annual chance of flooding plus storm waves, mapped by approximate methods.
VE (and older V1–V30) Coastal areas with a 1% annual chance of flooding and waves 3 feet or higher. A BFE is shown. These are the riskiest zones on the map.

Coastal A Zone. Some maps also show a Limit of Moderate Wave Action (LiMWA) line inside Zone AE near the coast. Land between that line and Zone VE can see waves 1.5 to 3 feet high, so building codes there often treat it more like a V zone.

Moderate and minimal risk zones

Zone What it means
X (shaded), or B on older maps Moderate risk. Areas between the 1% and 0.2% annual chance flood (the 500-year flood), plus some areas with 1% chance flooding less than 1 foot deep, small drainage areas, or land protected by a levee from the 1% chance flood.
X (unshaded), or C on older maps Minimal risk. Areas above the 0.2% annual chance flood.
D Possible but undetermined flood risk. No flood study has been done.
Open water A lake, river or ocean shown on the map.

Moderate and minimal risk doesn't mean no risk. Heavy rain, blocked drains, a broken water main or a storm bigger than the map's estimate can flood any building. More than 20% of flood insurance claims come from outside the high-risk zones.

What your zone means for insurance

  • In an A or V zone with a federally backed mortgage, your lender must require flood insurance on the building. This comes from the Flood Disaster Protection Act of 1973 and applies to loans from federally regulated or insured lenders, including FHA, VA and USDA loans.
  • In Zone X or D, flood insurance is usually optional. It also usually costs less, because the price reflects the lower estimated risk.
  • Anywhere, standard homeowners and renters policies don't cover flood damage. Flood insurance is a separate policy. See flood insurance basics.

Base flood elevation and why it matters

In zones with a BFE, the number that matters most is how high your lowest floor sits compared with it. A home built 2 feet above the BFE is far less likely to take on water than one built at it, and usually pays much less for flood insurance.

An elevation certificate records that comparison. It's completed by a licensed surveyor, engineer or architect. Your community's floodplain manager may already have one on file for your home, so ask before paying for a new one.

If you think your zone is wrong

Flood maps are drawn for whole areas, so a home built on higher ground can end up inside a high-risk zone on the map. You can ask FEMA to review it:

  • Letter of Map Amendment (LOMA). For a building on natural ground that sits above the BFE. FEMA doesn't charge to review a LOMA request, but you may need an elevation certificate or survey data.
  • Letter of Map Revision Based on Fill (LOMR-F). For land raised with fill above the BFE.
  • Letter of Map Revision (LOMR). For larger changes, such as a new flood study, usually requested by a community or developer.

Requests go through FEMA's Letter of Map Change process. If FEMA removes your building from the high-risk area, your lender is no longer required to make you carry flood insurance, though many owners keep it.

How to read the official map

Flood.global looks up your zone from FEMA's National Flood Hazard Layer, but the official source is the effective Flood Insurance Rate Map. To see it:

  1. Go to FEMA's Flood Map Service Center and search your address.
  2. Open the dynamic map or download the FIRMette, a one-page printable section of the official map.
  3. Check the effective date. Maps are updated over time, and preliminary maps for your area may show a future change.

Your community's floodplain manager, usually in the planning, building or public works department, can confirm your zone and answer questions about local building rules.

Sources