Flood Insurance Study: What It Contains and How to Use It

A Flood Insurance Study is the detailed technical report FEMA publishes to document flood risk along the rivers, lakes, and coastlines in a community, and it is the source document behind every Flood Insurance Rate Map. The study contains the Base Flood Elevations, flood profiles, and floodway data that determine whether your mortgage lender will require flood insurance and how high you have to build. The full reports are free to download from FEMA’s Map Service Center at msc.fema.gov.¹

What’s Inside the Report

Every FIS follows the same layout. The opening pages describe the community’s geography, major waterways, and history of significant flooding.² After that comes the technical core, which is what most readers are actually looking for.

The Summary of Discharges tables list the calculated volume of water expected to flow past specific points along each studied waterway during floods of different severity. The Flood Profiles section follows: graphs that plot water surface elevations along the centerline of each stream, usually showing the 10-year, 50-year, 100-year, and 500-year flood events along with the streambed elevation and the locations of road and bridge crossings.³

The Floodway Data Table rounds out the technical core. It lists specific cross-section locations along each waterway and provides the width, depth, velocity, and water surface elevation at each point. These are the numbers engineers pull when evaluating whether construction or fill inside the floodplain can meet local development standards.

Coastal communities get additional data. Coastal studies include transect analyses that model wave setup, wave height, wave runup, and overtopping, which are the primary drivers for mapping coastal high-hazard zones.⁴ Areas where wave runup reaches three feet or more above the ground surface are designated as VE Zones, the highest-risk coastal designation. Where wave effects fall below that threshold, the area is typically mapped as an AE Zone.

The Numbers That Drive Everything Else

The most consequential output of any FIS is the Base Flood Elevation. The base flood is the flood that has a one-percent chance of being equaled or exceeded in any given year, sometimes called the 100-year flood. The BFE is the predicted water surface height during that event, measured against a vertical reference point.⁵ Local building codes reference this single number when setting minimum construction elevations, and it is what triggers the federal flood insurance purchase requirement.

The study also establishes the Regulatory Floodway, defined as the channel of a river and the adjacent land that must remain unobstructed to carry the base flood without raising water levels beyond an allowable limit.⁶ Development inside the floodway faces the strictest restrictions. If a proposed project would cause any increase in the base flood elevation, it generally cannot be permitted.⁷

Check the Vertical Datum Before You Trust Any Elevation

Every elevation in an FIS is measured against a vertical datum, which is the reference surface that defines what “zero” means. Older studies used the National Geodetic Vertical Datum of 1929 (NGVD 29). The current standard is the North American Vertical Datum of 1988 (NAVD 88).⁸

The difference between the two varies by location, sometimes by several feet. If you compare a survey on your property using NAVD 88 against a BFE published under NGVD 29, the numbers won’t line up correctly. The FIS report and the title block of the corresponding FIRM both identify which datum applies. All new and updated FEMA maps must use NAVD 88, but plenty of older effective maps still reference NGVD 29, so this is a check that’s easy to skip and expensive to get wrong.⁸

How to Find and Download Your Study

The FEMA Flood Map Service Center at msc.fema.gov is the official public source for flood hazard products.¹ You can search by any of the following:

Property address, entered directly into the search field on the MSC homepage.
Community name, county, and state, which is useful for researching an area rather than a specific parcel.
The six-digit Community Identification Number FEMA assigns to each NFIP participant, which is the fastest route when community names are similar.⁹

After entering your search, select the option to view all available products. The results include FIS reports, FIRMs, and other flood hazard data. Open the FIS Reports folder and download the relevant volume. Large communities may have studies spanning several volumes, each covering a different geographic area, so check the volume descriptions. Reports come in PDF format.

Pay attention to whether a study is marked effective or preliminary. The effective study is the current legally binding document for insurance and floodplain management. A preliminary study represents proposed changes that haven’t completed the review and adoption process. Both can appear in search results, and confusing them leads to decisions based on data that hasn’t taken effect.

Reading the Profiles and Tables

The flood profiles are the most useful section for most property owners, and they’re where people tend to get lost. Each profile is a graph with distance along the stream on the horizontal axis and elevation on the vertical axis. Multiple lines represent different flood scenarios; the 100-year flood line is the one that establishes BFEs. Cross-section markers on the profile correspond to locations shown on the FIRM, and street crossings are labeled so you can orient yourself.

One detail matters more than it looks. Flood profiles are more precise than the FIRM. The rate map rounds BFEs to the nearest whole foot, while the profiles show elevation to tenths of a foot. For any construction or compliance decision where a fraction of a foot matters, the FIS profile is the authoritative source.³

The Floodway Data Table is the other section that gets heavy use. Each row represents a cross-section, and the columns give the floodway width, the area of the cross-section carrying flow, the mean water velocity, and the water surface elevation both with and without floodway encroachment. Engineers compare the two elevation columns to determine whether a proposed project would cause a prohibited increase in flood heights.

What the Study Means for Insurance and Building

The practical impact of an FIS comes down to two things: whether you have to buy flood insurance, and how you’re allowed to build.

Federal law prohibits lenders from issuing or renewing a mortgage on improved property in a Special Flood Hazard Area unless the borrower maintains flood insurance for the life of the loan. The coverage must equal at least the outstanding loan balance or the maximum available under the NFIP, whichever is less. Fannie Mae and Freddie Mac apply the same requirement to loans they purchase.¹⁰ The FIS and its companion FIRM are what determine whether your property sits inside one of those hazard areas.

On the construction side, communities participating in the NFIP must require that new residential buildings in AE and AH zones have their lowest floor, including any basement, elevated to or above the BFE. Nonresidential buildings can meet the standard through either elevation or dry floodproofing. In VE Zones along the coast, standards are stricter: buildings must be elevated on pilings or columns with the lowest floor above the BFE, and the area below must remain open to let waves pass through.⁷

FEMA’s current insurance pricing methodology, Risk Rating 2.0, incorporates more variables than the legacy system that relied heavily on flood zone designation. The new approach uses flood map data alongside distance to water, building characteristics, and historical claims to set premiums. Mapping data from the FIS remains a core input to the catastrophe models that drive pricing, and the mandatory purchase requirement still hinges on whether a property falls inside a Special Flood Hazard Area on the FIRM.¹¹

Elevation Certificates

An Elevation Certificate documents a building’s first-floor height and the surrounding grade elevations relative to the BFE from the FIS. Communities often require one before and after construction in flood-prone areas, and a property-specific certificate can affect your insurance premium by showing exactly how your building sits relative to the flood level. Elevation Certificates are also required when submitting a Letter of Map Change to revise flood zone designations on individual properties.¹² A licensed land surveyor or professional engineer prepares the certificate, and professional fees typically range from $150 to $750 depending on the property and location.

If You Think the Study Is Wrong About Your Property

Two different tools apply depending on whether the study you’re challenging is preliminary or already in effect.

For preliminary studies, you have 90 days from the second newspaper publication of FEMA’s proposed determination to file a formal appeal.¹³ The only grounds are that the proposed elevations are scientifically or technically incorrect. You need to identify the specific error in methodology, data, or measurements, and provide an alternative analysis prepared or certified by a registered professional engineer or licensed land surveyor. Arguing that the designation raises your insurance costs or lowers your property value is not a valid basis for appeal.¹⁴ Appeals don’t go directly to FEMA. You submit your written objection and supporting data to your community’s chief executive officer, such as the mayor, who consolidates all appeals from the community and forwards them.

For properties already shown in a Special Flood Hazard Area on an effective map, the appropriate tool is a Letter of Map Amendment. A LOMA fits when a property sits on natural ground at or above the BFE but was included in the flood zone because of the map’s scale limitations. To qualify, the lowest adjacent grade touching a structure must be at or above the BFE, or for undeveloped lots, the lowest point on the lot must meet that threshold. A licensed surveyor or professional engineer must certify the elevation data.¹⁵

FEMA typically completes its review and issues a determination within 60 days of receiving a complete application. A successful LOMA removes the mandatory insurance purchase requirement for the property, which can save thousands of dollars annually. Applications can be submitted through FEMA’s online LOMC portal or by mail.¹⁵

1
Federal Emergency Management Agency. FEMA Flood Map Service Center
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Federal Emergency Management Agency. About the Flood Insurance Study
3
Federal Emergency Management Agency. Flood Insurance Study Tutorial
4
Federal Emergency Management Agency. Guidance for Flood Risk Analysis and Mapping: Coastal Floodplain Mapping
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eCFR. 44 CFR 59.1 – Definitions
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Federal Emergency Management Agency. Floodway
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eCFR. 44 CFR 60.3 – Floodplain Management Criteria for Flood-Prone Areas
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Federal Emergency Management Agency. Guidance for Flood Risk Analysis and Mapping: Vertical Datum Conversion
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FEMA Independent Study. Lesson 2: Flood Map Basics – Section: Community Number or Countywide Number
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Office of the Law Revision Counsel. 42 USC 4012a – Flood Insurance Purchase and Compliance Requirements
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Federal Emergency Management Agency. NFIP’s Pricing Approach
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Federal Emergency Management Agency. Understanding Elevation Certificates
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eCFR. 44 CFR Part 67 – Appeals from Proposed Flood Elevation Determinations
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Federal Emergency Management Agency. Appeals and Comments: Information for Property Owners
15
Federal Emergency Management Agency. Letter of Map Amendment and Letter of Map Revision-Based on Fill