Section 27-2077. Conversions to rooming units prohibited

a. No rooming unit
  which was not classified and recorded as such in the department prior to
  May fifteenth, nineteen hundred fifty-four  or  converted  to  such  use
  prior  to  April thirtieth, nineteen hundred fifty-six, shall be created
  in any dwelling, whether such conversion is  effected  with  or  without
  physical alterations, except for rooming units:
    (1)  Owned  or  controlled and operated by a hospital for occupancy by
  nurses and interns on its staff; or
    (2) Owned and operated without profit by an educational, religious  or
  charitable institution as a residence for the aged, or for working girls
  or  women,  or  for working boys or men, or for delinquent, dependent or
  neglected children, or for students attending a school or college; or,
    (3) approved by the commissioner of the department  and  created  with
  the  substantial  assistance  of  loans,  grants  or  subsidies from any
  federal, state or local agency or instrumentality; or
    (4) approved by the commissioner of the department and owned, operated
  or used by any federal, state or local agency or instrumentality or by a
  non-profit organization.
    b. When the ownership, operation or use by an  institution  or  public
  agency  for  any of the purposes enumerated in subdivision a ceases, the
  certificate of occupancy shall expire.