N.Y.C. Admin. Code § 27-2084: § 27-2084 Occupancy of cellars and basements in converted dwellings.

a. Except as provided in 27-2082 of this article, no dwelling unit in the cellar of a converted dwelling may be occupied for living purposes unless:

(1) The yard adjoining such dwelling unit; has a minimum depth of thirty feet or more at every point; is open and unobstructed except as permitted by subdivision nine of section twenty-six of the multiple dwelling law; and abuts the exterior wall of such dwelling at a level no higher than the floor of any room contained in the dwelling unit; and

(2) The department determines that the dwelling unit is habitable. Such a cellar shall be deemed a basement for the purpose of all requirements of the multiple dwelling law and of this code.

b. Except as provided in section 27-2082 of this article, no dwelling unit in the basement of a converted dwelling may be occupied unless:

(1) Every living room has a minimum height of seven feet in every part; and

(2) Every living room has at least one window which complies with the provisions of subdivision b of section 27-2059 of article one of this subchapter, except that the top of at least one window shall be a minimum of six feet above the floor, or if the room does not comply with the foregoing provisions of this paragraph two, it complies with the provisions of subdivision c of section 27-2059 of article one of this subchapter.

c. The basement of a dwelling converted in accordance with the provisions of subdivision four of section one hundred seventy-seven of the multiple dwelling law may be occupied only if the dwelling is classified and recorded in the department as such a converted dwelling prior to January first, nineteen hundred sixty-six.