D.C. Mun. Regs. tit. 20, § 3199
When used in this chapter, the following words and phrases shall have the meanings ascribed:
Accessory Structure – a structure that is:
Adjacent community – any State, or political subdivision thereof, that is immediately adjacent to the borders of the District of Columbia and that has authority to adopt and enforce floodplain management regulations for areas inside its jurisdiction.
Alteration of a watercourse – a dam, impoundment, channel relocation, change in channel alignment, channelization, or change in cross-sectional area of the channel or the channel capacity, or any other form of modification, which may alter, impede, retard, or change the direction or velocity of the riverine flow of water during conditions of the base flood.
Ancillary residential use portion – a portion of a building that is used by residents, but not as a residential unit. Ancillary residential uses include lobbies, mailrooms, loading docks, and gyms that are available only to residents, but do not include above-grade enclosed areas that are below the DFE and used solely for parking of vehicles, building access, or storage.
American Society of Civil Engineers Standard 24-14 (ASCE 24), Flood Resistant Design and Construction – a publication of the American Society of Civil Engineers (ASCE) that provides minimum requirements for flood-resistant design and construction of structures located in flood hazard areas. FEMA has deemed that ASCE 24 meets or exceeds the minimum National Flood Insurance Program requirements for buildings and structures. ASCE 24 is a referenced standard in the International and District of Columbia Construction Codes. ASCE 24-14 refers to the version of ASCE 24 published in 2014 that is available on the ASCE website at: https://ascelibrary.org/doi/book/10.1061/9780784413791.
Base flood – the flood having a one percent (1%) chance of being equaled or exceeded in any given year. The base flood is commonly referred to as the “one hundred (100)-year flood” or the “one-percent (1%)-annual-chance flood.”
Base floodplain – the area that would be inundated by a flood having a one percent (1%) chance of being equaled or exceeded in any given year, also known as the one hundred (100)-year floodplain.
Base flood elevation – the one hundred (100)-year flood elevation, including wave height,
relative to the National Geodetic Vertical Datum (NGVD), North America Vertical Datum (NAVD), or other datum specified on the Flood Insurance Rate Map (FIRM).
Basement - the portion of a building having its floor subgrade (below ground level) on all sides.
Construction – the building, rebuilding, renovation, repair, extension, expansion, alteration, or relocation of a structure.
Critical facility – a building or structure intended to remain operational in the event of extreme environmental loading from flood, wind, snow, or earthquake that contains essential equipment, houses services necessary for emergency response and recovery, or would pose a substantial risk to the public or significant disruption to the community at large in the event of failure, disruption of function during or after flooding, or damage by flooding. Critical facilities include:
(k) Elementary schools and secondary schools;
(l) Preschool and child care facilities not located in one- and two-family dwellings;
Design Flood Elevation (DFE) – the one hundred (100)-year flood elevation (base flood elevation) plus two feet (2 ft.), or the five hundred (500)-year flood elevation (high flood elevation), whichever is higher, based on the FEMA Flood Insurance Rate Map, effective September 27, 2010, and subsequent revisions and amendments as approved by FEMA, or the flood protection elevation as designated herein in accordance with the Floodplain Management Regulations.
Development – any human-made change to improved or unimproved premises, including buildings or other structures, temporary structures, temporary or permanent storage of materials, mining, dredging, filling, grading, paving, excavations, operations, and other land-disturbing activities.
Development Site – a record lot located wholly or partially inside a flood hazard area on which any development is proposed to occur.
District-registered professional engineer – an engineer who registers as a professional engineer and becomes licensed to practice as an engineer in the District of Columbia.
District of Columbia (D.C.) Building Code – the District of Columbia Building Code Supplement, 12-A DCMR, or any successor thereto.
District of Columbia (D.C.) Construction Codes – the District of Columbia Construction Codes Supplement, 12-A DCMR, and any subsequent editions thereof, or any successor thereto.
DOB – the District of Columbia Department of Buildings.
DOEE – the Department of Energy and Environment.
Dry floodproofing – a combination of design modifications that result in a building or structure, including the attendant utility and sanitary facilities, being watertight with walls substantially impermeable to the passage of water and with structural components having the capacity to resist hydrostatic loads.
Elevation Certificate – the National Flood Insurance Program Elevation Certificate (FEMA
form 086-0-33), any successor to FEMA form 086-0-33, or other DOEE-approved form used to certify that new buildings and substantial improvements in flood hazard areas are properly elevated in accordance with the Floodplain Management Regulations.
Enclosure – an area below the lowest floor of an elevated building that is enclosed on all sides by walls.
Encroachment – the placement of fill, excavation, buildings, permanent structures, or other development into a flood hazard area that may impede or alter the flow capacity of riverine flood hazard areas.
Existing manufactured home park or subdivision – a manufactured home park or subdivision for which the construction of facilities for servicing the lots on which the manufactured homes are to be affixed (including, at a minimum, the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads) is finished before the effective date of the Floodplain Management Regulations adopted by the District of Columbia.
Expansion to an existing manufactured home park or subdivision – the preparation of additional sites by the construction of facilities for servicing the lots on which the manufactured homes are to be affixed (including the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads).
FEMA – the Federal Emergency Management Agency.
Flood or flooding – a general and temporary condition of partial or complete inundation of normally dry land from:
(b) The unusual and rapid accumulation or runoff of surface waters from any source.
Flood hazard area – the land inside the five hundred (500)-year (Zone X(shaded)) or one hundred (100)-year (Zones A, AE, A1-30, A99, AR, AO, or AH) floodplain in accordance with the FEMA Flood Insurance Rate Map, effective September 27, 2010, and subsequent revisions and amendments as approved by FEMA, or other area designated herein as a flood hazard area in accordance with the Floodplain Management Regulations.
Flood Insurance Rate Map (FIRM) – an official map of a community on which FEMA has delineated both the flood hazard areas and other risk premium zones applicable to the community.
Flood Insurance Study (FIS) – the official report provided by FEMA containing the Flood Insurance Rate Map (FIRM), the Flood Boundary and Floodway Map (FBFM), the water surface elevation of the base flood, and supporting technical data.
Floodplain – a relatively flat or low land area that is subject to partial or complete inundation from an adjoining or nearby stream, river, or watercourse; or any area subject to the usual and rapid accumulation of surface waters from any source.
Floodplain Management Regulations – The flood-resistant construction provisions of the D.C. Construction Codes, in combination with this chapter.
Floodproofing – any combination of structural and nonstructural additions, changes, or adjustments to structures that reduce or eliminate flood damage to real estate or improved real property, water and sanitary facilities, structures, and their contents.
Floodproofing Certificate – the National Flood Insurance Program Floodproofing Certificate for Non-Residential Structures (FEMA form 086-0-34), any successor to FEMA form 086-0-34, or other DOEE approved form used to certify a floodproofing design for buildings that are permitted by these regulations to use dry floodproofing as an alternative to elevating to or above the DFE.
Floodway – the channel of a river, creek, or other watercourse and the adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than a designated height.
Freeboard – a factor of safety usually expressed in feet above a flood level for purposes of floodplain management intended to compensate for the many unknown factors that could contribute to flood heights greater than the height calculated for a selected size flood and floodway conditions, such as wave action, bridge openings, and the hydrological effect of urbanization of the watershed.
Hazardous Materials – The following materials:
(h) Hydrochloric acid;
(i) Hydrocyanic acid;
(j) Magnesium;
(k) Nitric acid and oxides of nitrogen;
(l) Petroleum products (gasoline, fuel oil, etc.);
(m) Phosphorus;
(n) Potassium;
(o) Sodium;
(p) Sulfur and sulfur products;
(q) Pesticides (including insecticides, fungicides, and rodenticides); and
(r) Radioactive substances.
High flood – the flood having a two-tenths percent (0.2%) chance of being equaled or exceeded in any given year, also known as the five-hundred (500)-year flood.
High flood elevation – the five hundred (500)-year flood water surface elevation, including wave height, relative to the National Geodetic Vertical Datum (NGVD), North America Vertical Datum (NAVD), or other datum specified on the Flood Insurance Rate Map (FIRM).
Historic structure – any structure that is:
(a) Individually listed in the National Register of Historic Places (a listing maintained by the U.S. Department of Interior) or preliminarily determined by the Secretary of the Interior as meeting the requirements for individual listing on the National Register;
(b) Certified or preliminarily determined by the Secretary of the Interior as contributing to the historical significance of a registered historic district or a district preliminarily determined by the Secretary to qualify as a registered historic district;
(c) Individually listed on a state inventory of historic places in states with historic preservation programs that have been approved by the Secretary of the Interior; or
(d) Individually listed on a local inventory of historic places in communities with historic preservation programs that have been certified either:
a. By an approved state program as determined by the Secretary of the Interior; or
b. Directly by the Secretary of the Interior in states without approved programs.
Hydrologic and Hydraulic (H&H) Analysis – an analysis that quantifies the volumetric flow of water. Hydraulic analyses determine the depth of flow, flow velocity, and forces from flowing water.
Interior Flooding – Floods, also known as flash floods, urban floods, stormwater floods, and cloudburst floods, that are caused by heavy rainfall that cannot be absorbed by the ground and then overwhelm the drainage system. Interior flooding can occur when river elevations are normal because interior floods are attributed to topography, development, localized weather, and the capacity of stormwater systems. Generally, areas of interior flood risk are not mapped on FEMA’s flood insurance rate maps.
Land-disturbing activity – Movement of earth, land, or sediment that disturbs the land surface and the related use of pervious land to support that movement. Land-disturbing activity includes stripping, grading, grubbing, trenching, excavating, transporting, and filling of land, as well as the use of pervious adjacent land for movement and storage of construction vehicles and materials. Land-disturbing activity does not include repaving or remilling that does not expose the underlying soil.
Letter of Map Change – an official determination issued by FEMA that amends or revises an effective Flood Insurance Rate Map or Flood Insurance Study. Letters of Map Change include:
(a) Letter of Map Amendment (LOMA) – An amendment based on technical data showing that a property was incorrectly included in a designated special flood hazard area. A LOMA amends the current effective Flood Insurance Rate Map and establishes that a specific property, portion of a property, or structure is not located in a special flood hazard area.
(b) Letter of Map Revision (LOMR)– A revision based on technical data that may show changes to flood zones, flood elevations, special flood hazard area boundaries and floodway delineations, and other planimetric features.
(c) Letter of Map Revision Based on Fill (LOMR-F) – A determination that a structure or parcel of land has been elevated by fill above the base flood elevation and is, therefore, no longer located inside the special flood hazard area. In order to qualify for this determination, the fill must have been permitted and placed in accordance with the community’s floodplain management regulations.
(d) Conditional Letter of Map Revision (CLOMR) – A formal review and comment as to whether a proposed flood protection project or other project complies with the minimum NFIP requirements for the projects with respect to delineation of special flood hazard areas. A CLOMR does not revise the effective Flood Insurance Rate Map or Flood Insurance Study; upon submission and approval of certified as-built documentation, a Letter of Map Revision may be issued by FEMA to revise the effective FIRM.
Lowest floor – the floor of the lowest enclosed area, including basement. The term excludes the floor of any unfinished or flood-resistant enclosure usable solely for vehicle parking, building access or limited storage provided that the enclosure is not built so as to render the structure in violation of Section 1612 of the D.C. Building Code and Appendix G 12-A DCMR.
Manufactured home – a structure that is transportable in one or more sections, built on a permanent chassis, designed for use with or without a permanent foundation when attached to the required utilities, and constructed to the Federal Manufactured Home Construction and Safety Standards and rules and regulations promulgated by the U.S. Department of Housing and Urban Development in 24 CFR Part 3280. The term also includes mobile homes, park trailers, travel trailers and similar transportable structures that are placed on a site for one hundred eighty (180) consecutive days or longer.
Mixed-use building – any building or structure that has non-residential and residential portions.
National Flood Insurance Program (NFIP) – a Federal program administered by FEMA enabling property owners in participating communities to purchase insurance protection against losses from flooding. Participation in the NFIP is based on an agreement between local communities and FEMA under which FEMA agrees to make flood insurance available in the community as a financial protection against flood losses if the community will adopt and enforce a floodplain management ordinance to reduce future flood risks from new construction and development in flood hazard areas.
NAVD88 – the North American Vertical Datum of 1988 (NAVD88) which is the current vertical control datum for the District of Columbia. It defines a specific zero (0) elevation point from which vertical elevation is measured.
New construction – site preparation for, and construction of, entirely new structures and structures that maintain only the existing foundation, the exterior walls, or both. New construction means, for the purposes of determining insurance rates, structures for which the “start of construction” started on or after the effective date of an initial FIRM or after December 31, 1974, whichever is later, and includes any subsequent improvements to the structures. For floodplain management purposes, new construction means structures for which the start of construction started on or after the effective date of a floodplain management regulation adopted by the District and includes any subsequent improvements to the structures.
New manufactured home park or subdivision – a manufactured home park or subdivision for which the construction of facilities for servicing the lots on which the manufactured homes are to be affixed (including at a minimum, the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads) is finished on or after the effective date of these regulations.
No-Rise Certification – a document that the applicant provides to demonstrate that their project does not cause any increase to the base flood elevation.
Non-residential – any building or structure or portion thereof that is not classified residential.
Non-residential portion of a mixed-use building – a portion of the mixed-use building that is available for use by the general public or is publicly accessible.
Recreational vehicle – a vehicle that is built on a single chassis, four hundred square feet (400 sq. ft.) (thirty-seven and sixteen hundredths square meters (37.16 m2)) or less when measured at the largest horizontal projection, designed to be self-propelled or permanently towable by a light-duty truck, and designed primarily not for use as a permanent dwelling but as temporary living quarters for recreational, camping, travel, or seasonal use. A recreational vehicle is ready for highway use if it is on its wheels or jacking system, is attached to the site only by quick disconnect-type utilities and security devices and has no permanently attached additions.
Registered Design Professional – an individual who is registered or licensed to practice engineering, architecture, or land surveying, as defined by the statutory requirements of the professional registration laws of District of Columbia.
Residential – refers to:
Residential portion of a mixed-use building – residential or dwelling unit where people live or that are used for sleeping purposes. Ancillary residential uses such as lobbies, mailrooms, loading docks, and gyms that are available only to residents inside the residential portion of a mixed-use building.
Resilient systems plan – a suitability assessment of equipment and systems that support critical functions of the facility and that specifies flood mitigation measures that will be taken to protect the systems.
Resubmission – after the initial submission of a permit application by an applicant to DOEE, each time the applicant makes changes to, or provides new information for their application (including at the request of DOEE), is considered a resubmission.
Special flood hazard area – the land area subject to flood hazards and shown on a Flood Insurance Rate Map or other flood hazard map as Zone A, AE, A1-30, A99, AR, AO, AH, V, VO, VE, or V1-30.
Start of construction – the date of permit issuance for new construction and substantial improvements to existing structures, provided the actual start of construction, repair, reconstruction, rehabilitation, addition, placement, or other improvement is within one hundred eighty (180) days after the date of issuance. The actual start of construction means the first placement of permanent construction of a building (including a manufactured home) on a site, such as the pouring of a slab or footings, installation of pilings, or construction of columns. Permanent construction does not include land preparation (such as clearing, excavation, grading or filling), the installation of streets or walkways, excavation for a basement, footings, piers or foundations, the erection of temporary forms or the installation of accessory buildings such as garages or sheds not occupied as dwelling units or not part of the main building. For a substantial improvement, the actual start of construction means the first alteration of any wall, ceiling, floor, or other structural part of a building, whether or not that alteration affects the external dimensions of the building.
Structure – for floodplain management purposes, a walled and roofed building, including a gas or liquid storage tank, that is principally above ground, as well as a manufactured home or recreational vehicle that is on-site for more than one hundred eighty (180) days.
Subdivision – the division or assembly of land into one or more lots of record that are platted and recorded on the records of the Surveyor in accordance with the Subdivision Regulations of the District of Columbia, 10B DCMR §§ 2700 et seq.
Substantial damage – damage of any origin sustained by a structure for which the cost of restoring the structure to the condition before the damage occurred would equal or exceed 50 percent (50%) of the tax assessed value of the structure before the damage occurred.
Substantial improvement – any combination of repairs, reconstruction, rehabilitation, additions, modifications, or improvements of a building or structure made during the five (5)-year period immediately preceding a permit application, the aggregate cost of which, together with the cost of the work proposed by the latest permit application, equals or exceeds fifty percent (50%) of the tax assessed value of the structure before the start of construction. If the structure has sustained substantial damage, any repairs are considered substantial improvement regardless of the actual repair work performed. The term does not include:
Tidal shoreline buffer – land projected to be inundated by water by year 2080 due to changes in sea level as determined by best available science. The flood hazard area is the land inside the Tidal Shoreline Buffer layer depicted in the DOEE Flood Risk Portal (http://dcfloodrisk.org/), along with any subsequent revisions and amendments.
Watercourse – A river, creek, stream, channel, or other topographic feature in, on, through, or over which water flows at least periodically.
Wet floodproofing – floodproofing method that relies on the use of flood-damage-resistant materials and construction techniques to minimize flood damages to areas below the DFE of a structure intentionally allowed to flood.
SOURCE: Final Rulemaking published at 32 DCR 6547, 6562 (November 15, 1985); as amended by Final Rulemaking published at 35 DCR 962, 963 (February 12, 1988); as amended by Notice of Final Rulemaking published at 57 DCR 10782 (November 19, 2010); as amended by Final Rulemaking published at 72 DCR 006821 (June 20, 2025).