Applicants proposing to change the headroom of an existing basement or cellar with substandard but pre-existing structural headroom of over six feet, six inches (6 ft., 6 in.) must determine if such change constitutes an addition under the Zoning Regulations.  The relevant definitions are set forth as follows:   

Definitions: 11 DCMR § B-100.2 

Cellar:  That portion of a story partly below grade where the finished floor of the ground floor is less than five feet (5 ft.) above the adjacent natural or finished grade, whichever is the lower elevation. 

Basement:  That portion of a story partly below grade where the finished floor of the ground floor is five feet (5 ft.) or more above the adjacent natural or finished grade, whichever is the lower in elevation.   

The change in the headroom space of a basement or cellar over 6 feet 6 inches will not be considered an addition because the pre-existing condition is considered to be existing cellar or basement floor area.  However, the horizontal area of a basement is included in the Gross Floor Area (GFA) calculation per Section B-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). . . 

Therefore, the Zoning Administrator has determined that an increase in the headroom space of a basement or cellar where the pre-existing structural headroom is six feet, six inches (6 ft., 6 in.) or greater is not considered an addition nor an expansion of Gross Floor Area or cellar area.   

As an example, an increase in the headroom space or vertical clearance for a basement from seven (7) feet to nine (9) feet would be a permissible change not deemed an addition.