304. RULES OF MEASUREMENT FOR GROSS FLOOR AREA (GFA)

304 RULES OF MEASUREMENT FOR GROSS FLOOR AREA (GFA) 304.1 GFA is measured from the exterior faces of exterior walls and from the center line of walls separating two (2) buildings. 304.2 Except as provided in Subtitle I § 200.1, non-residential floor area shall be the total GFA of a building not dedicated to one (1) of the following uses: Residential; (b) Community-based institutional facility; (c) Emergency shelter; (d) Lodging use with less than thirty (30) rooms; (e) Guest rooms and service areas of a lodging use with thirty (30) or more rooms; or (f) Education uses that are operated or chartered by the District government. 304.3 The GFA of a lodging use dedicated to function rooms, exhibit space, commercial adjuncts and any other use not considered guest room or service area shall be considered non-residential floor area. 304.4 For a building entirely detached from any other building, GFA for the portion of a story located below the finished floor of the ground floor and partly above adjacent natural or finished grade shall be calculated by the perimeter-wall method, which is as follows: (a) Measure the portions of the perimeter of the story below the finished floor of the ground floor that are five feet (5 ft.) or more above the adjacent natural or finished grade, whichever is the lower elevation; (b) Measure the total perimeter of the story located below the finished floor of the ground floor; (c) Divide the distance of the result of paragraph (a) by the distance of the result of paragraph (b); and (d) Multiply result from paragraph (c) by the total floor area of the story located below the finished floor of the ground floor. 304.5 For a semi-detached or attached building, GFA for the portion of a story below the finished floor of the ground floor and partly above adjacent natural or finished grade shall be calculated by the grade-plane method, which is as follows: For the purposes of this measurement, a building’s “front façade” is the façade facing the nearest street and a building’s “opposite face” is the portion of the building that faces the opposite direction of the front façade; Establish a line between the midpoint of a building’s front façade at the adjacent natural or finished grade, whichever is the lower elevation, and the midpoint of the building’s opposite face at the adjacent natural or finished grade, whichever is the lower in elevation, subject to paragraph (c); If excavations project from the building’s front façade or opposite face that are not an exception to grade, as defined at 11-B DCMR § 100.2, the elevation of the midpoint of the building front façade shall be the equivalent of the lowest such elevation; excluding existing driveways adjacent to the midpoint(s) directly connecting a garage and public right of way; Determine the portion of this line that is five feet (5 ft.) or more below the finished floor of the ground; Project a perpendicular line from the point along the line described in paragraph (d) to the exterior walls of the building; and Measure the floor area that is between the projected perpendicular line and the portions of the story five feet (5 ft.) or more below the finished floor of the ground floor. 304.6 For a building where the finished floor of the ground floor is removed or altered in elevation in association with a renovation where a raze of the building has not occurred, the higher of previously existing or new finished floor of the ground floor shall be used for calculating the gross floor area pursuant to 11-B DCMR §§ 304.4 and 304.5. 304.7 GFA shall include basements, elevator shafts, and stairwells at each story; floor space used for mechanical equipment (with structural headroom of six feet, six inches (6 ft., 6 in.), or more); penthouses or rooftop structures (unless otherwise specified); attic space (whether or not a floor has actually been laid, provided structural headroom of six feet, six inches (6 ft., 6 in.), or more); interior balconies; and mezzanines. 304.8 GFA shall not include: (a) Cellars, (b) Exterior balconies that do not exceed a projection of eight feet (8 ft.) beyond the exterior walls of the building; (c) Inset balconies open and unenclosed on at least one side, to a maximum depth of eight feet (8 ft.) in from the adjacent exterior façade of the building; (d) All projections beyond the lot line that may be allowed by other Municipal codes; (e) All projections beyond the lot line that may be allowed by other Municipal codes; (f) Vent shafts, and pipe chase shafts above the ground floor; (g) Atriums above the ground floor; (h) Ramps on the ground floor leading down to areas of parking on a lower level; and (i) In residential zones, the first floor or basement area designed and used for parking or recreation spaces provided that not more than fifty percent (50%) of the perimeter of that space may be comprised of columns, piers, walls, or windows, or similarly enclosed. SOURCE: Final Rulemaking published at 63 DCR 2447, 2650 (March 4, 2016 – Part 2); as amended by Final Rulemaking published at 65 DCR 8555 (August 17, 2018); as amended by Final Rulemaking published at 65 DCR 11934 (October 26, 2018); as amended by Final Rulemaking published at 66 DCR 71 (January 4, 2019); as amended by Final Rulemaking published at 68 DCR 013834 (December 24, 2021); as amended by Final Rulemaking published at 73 DCR 009999 (July 10, 2026). District of Columbia Municipal Regulations Zoning Regulations of 2016: Definitions, Rules of Measurement, and Use Categories 11-B DCMR § 304