Definition: open space (General Definition)
"Open space" is that part of a zoning lot , including courts or yards , which is open and unobstructed from its lowest level to the sky and is accessible to and usable by all persons occupying a dwelling unit or a rooming unit on the zoning lot . Open space may, however, include areas covered by roofs, the total area of which is less than 10 percent of the unroofed or uncovered area of a zoning lot , provided that such roofed area is not enclosed on more than one side, or on more than 10 percent of the perimeter of the roofed area, whichever is greater. Open space may be provided on the roof of: (a) a community facility building ; (b) a building containing residences , provided such roof area is not above that portion of such building that contains dwelling units or rooming units ; (c) a non-residential building , other than a community facility building , provided such non-residential building abuts other buildings , any one of which contains residences . All such roof areas used for open space shall meet the requirements set forth in this definition and shall: (1) be not higher than 23 feet above curb level , except as provided in Sections 24-181 (Special provisions for certain buildings) and 35-712 (Floor area and open space ratios); (2) be at least two and one-half feet below the sill level of all legally required windows opening on such roof area; (3) be directly accessible by a passageway from a building , or by a ramp (with a grade of less than 10 percent) from a building , yard , court or street , except that in R8 or R9 Districts such roof area need not be accessible to occupants and is therefore exempt from this requirement; and (4) have no dimension less than 25 feet; except that in R8 or R9 Districts when such roof area adjoins a street line or a rear yard , it may have a minimum depth of nine feet and a minimum length, along such street line or rear yard , equal to at least twice its depth, or the full width of the zoning lot , or 50 feet, whichever is the least distance.