A Letter of Map Revision is required whenever a human-made change to the landscape, or new engineering data, makes FEMA’s current Flood Insurance Rate Map inaccurate for a property or area. If someone places fill, builds or modifies a levee, replaces a bridge or culvert, reshapes a channel, or develops in the floodplain in a way that changes how floodwater behaves, the official map no longer reflects reality and a LOMR is the tool that fixes it. FEMA won’t update the map on its own; the property owner, developer, or community has to apply.
Situations That Trigger a LOMR
FEMA groups the triggers as physical or climatic changes that affect the flood hazard data shown on a FIRM.1Federal Emergency Management Agency. When Is a Letter of Map Revision (LOMR) Required? In practice, the common situations are:
- Placing fill to raise a property or structure above the Base Flood Elevation. This is handled through a specific track called a LOMR-F (Letter of Map Revision Based on Fill) and is the simplest type of revision.2FEMA.gov. Letter of Map Amendment and Letter of Map Revision-Based on Fill Process
- Building or modifying flood control structures such as levees, dams, berms, or floodwalls that change how floodwater is contained or redirected.
- Installing a new bridge or culvert, or replacing an existing one, which alters how water flows under or through the crossing.
- Dredging, straightening, or otherwise reshaping a waterway in ways that change flood flow patterns.
- Producing updated hydrologic or hydraulic studies that show different flood elevations or floodway boundaries than the current map reflects.
- Constructing or grading in the floodplain in ways that significantly change flood depths, extents, or flow paths.
The common thread is that something on the ground has changed, or new technical data proves the map is no longer correct. If neither is true, a LOMR is not the right instrument.
When You Actually Need a LOMA Instead
The most common mistake is confusing a LOMR with a Letter of Map Amendment. A LOMA corrects a mapping error: your property sits on naturally high ground but FEMA’s map wrongly places it in a Special Flood Hazard Area. Nothing physical changed; the map was just wrong. LOMAs carry no FEMA review fee.2FEMA.gov. Letter of Map Amendment and Letter of Map Revision-Based on Fill Process
A LOMR, by contrast, acknowledges that flood risk genuinely changed because of something people did. That distinction drives everything else about the process, because LOMRs require engineering analysis and carry review fees, while LOMAs are simpler administrative corrections.3FEMA. Letters of Map Revision and Conditional Letters of Map Revision If you’re asking whether the ground truly changed or the map was simply wrong from the start, the answer decides which application you file.
When You Need FEMA’s Sign-Off Before You Build
For larger projects, you cannot build first and apply for the map revision afterward. A Conditional Letter of Map Revision, or CLOMR, is FEMA’s advance review of a proposed project. It amounts to FEMA saying that if the project is built exactly as designed, it would meet National Flood Insurance Program standards and the map change would likely be approved.3FEMA. Letters of Map Revision and Conditional Letters of Map Revision
A CLOMR becomes legally required when a community proposes to permit development in a regulatory floodway that would increase the base flood elevation beyond what NFIP regulations allow. In that situation, the community must apply to FEMA for conditional approval before issuing permits. The application has to include an evaluation of alternatives that would not raise flood levels, documentation that all affected property owners have been individually notified, and concurrence from the chief executive of any other community affected by the project.4eCFR. 44 CFR 65.12 – Revision of Flood Insurance Rate Maps to Reflect Base Flood Elevations Caused by Proposed Encroachments
Skipping the CLOMR step when it’s required can put a community’s entire NFIP participation at risk, which would block every property owner in that jurisdiction from buying federal flood insurance.4eCFR. 44 CFR 65.12 – Revision of Flood Insurance Rate Maps to Reflect Base Flood Elevations Caused by Proposed Encroachments After the conditional approval, the community submits as-built certifications so FEMA can process the final LOMR.
Extra Requirement for Floodway Projects
If the work sits inside a regulatory floodway, there is an added hurdle before the LOMR question even comes up. Any development in a floodway requires an engineering analysis demonstrating the project will not increase flood heights, documented in a no-rise certification signed by a registered professional engineer. The certification has to be supported by technical data based on the same hydraulic modeling FEMA used to establish the floodway on the current map.5FEMA.gov. No-Rise Certification for Floodways
The certification must be complete before the local community can issue a permit. It is separate from the LOMR application itself, but the same engineering analysis usually feeds directly into the LOMR submission. A floodway project that cannot demonstrate zero rise faces a much more complicated path and may trigger the CLOMR process.
What Filing Costs and What You Need
FEMA charges a review fee on every LOMR and CLOMR request, and the amount depends on the type of change. The current schedule, in effect since February 2015:
- LOMR-F for a single lot or structure: $425 online, $525 by paper.
- LOMR based on a bridge, culvert, channel, hydrology, or a combination: $8,000 online, $8,250 by paper.
- LOMR based on a levee, berm, or other structural measures: $9,000 online plus $60 per hour of review time, or $9,250 by paper plus $60 per hour.
- CLOMR based on hydrology, bridge, culvert, or channel: $6,500 online, $6,750 by paper.
- CLOMR based on a levee, berm, or structural measures: $7,000 online plus $60 per hour, or $7,250 by paper plus $60 per hour.
When a project falls into more than one category, the highest applicable fee applies.6FEMA.gov. Flood Map-Related Fees Final LOMRs also carry a $35 charge covering FEMA’s cost of physically revising the affected FIRM panels.7eCFR. 44 CFR Part 72 – Procedures and Fees for Processing Map Changes
Applications use FEMA’s MT-2 form series. Beyond a simple LOMR-F, plan on hiring a licensed professional engineer, because the hydrologic and hydraulic modeling, no-rise certifications, and technical analyses supporting the request have to be prepared and certified by a PE. Elevation certificates and topographic surveys usually mean a surveyor as well. Those professional fees vary widely with project scope and location and commonly run from several hundred to several thousand dollars on top of the FEMA charge.
One requirement catches applicants off guard: the local community’s chief executive officer, or their designee, must sign off on the request. Federal regulations require LOMRs based on new technical data to be submitted through the community CEO. If the CEO refuses to submit on your behalf, FEMA will still review the application, but only if you provide written evidence that you asked the community to participate and they declined.8Federal Emergency Management Agency. Instructions for MT-2 Forms
What Changes for Flood Insurance
For many applicants, the reason to pursue a LOMR or LOMR-F is removing a property from the Special Flood Hazard Area so the federal flood insurance mandate goes away. If you have a federally backed mortgage on a property inside the SFHA, your lender is required to make you carry flood insurance. Once FEMA issues a LOMA or LOMR-F removing the property from the SFHA, that federal purchase requirement is eliminated.2FEMA.gov. Letter of Map Amendment and Letter of Map Revision-Based on Fill Process A lender can still choose to require coverage on its own, but premiums for properties outside the SFHA are meaningfully lower than for those inside it.