Gaithersburg, MD Environmental Rules: Flood Zones (2026)

Gaithersburg participates in the National Flood Insurance Program (NFIP) and enforces floodplain management standards that meet or exceed FEMA minimum requirements. The city has significant flood-prone areas along Muddy Branch, Great Seneca Creek, and other waterways. FEMA Flood Insurance Rate Maps (FIRMs) identify Special Flood Hazard Areas (SFHAs) within the city. All development in the SFHA requires a floodplain development permit from the city. New residential construction must have the lowest floor, including basement, elevated at least 1 foot above the base flood elevation (BFE), which exceeds the FEMA minimum of at or above the BFE. Non-residential structures may be floodproofed to that level as an alternative. Substantial improvements, defined as repairs, renovations, or additions whose cost equals or exceeds 50 percent of the structure's pre-improvement market value, must bring the entire structure into compliance with current floodplain standards. Fill in the floodplain is restricted and must not reduce flood storage capacity or increase flood levels on adjacent properties. Montgomery County also regulates stream valley buffers that may extend beyond the FEMA-mapped floodplain. The city's comprehensive plan identifies flood mitigation as a priority. Flood insurance is required for federally backed mortgages on properties in the SFHA. Contact the Department of Planning and Code Administration at (301) 258-6330 for floodplain determination and permit requirements.