Section 25-321. Applicability

The  provisions  of  this  chapter shall be
  inapplicable  to  the  construction,   reconstruction,   alteration   or
  demolition  of  any  improvement  on  a  landmark  site or in a historic
  district or containing an interior landmark, or of any landscape feature
  of a scenic landmark, where a permit for the performance  of  such  work
  was  issued  by  the  department  of  buildings,  or,  in  the case of a
  landscape feature of a scenic landmark, where plans for such  work  have
  been  approved,  prior  to  the  effective  date  of the designation, or
  amended or modified designation, pursuant to the provisions  of  section
  25-303  of  this  chapter,  first  making the provisions of this chapter
  applicable  to  such  improvement  or  landscape  feature  or   to   the
  improvement  parcel  or  property in which such improvement or landscape
  feature is or is to be located.