Section 27-111. Continuation of lawful existing use

The lawful occupancy and
  use of any building, including the use of any service equipment therein,
  existing on the effective date of this code or thereafter constructed or
  installed  in  accordance  with  prior code requirements, as provided in
  section 27-105 of article one  of  this  subchapter,  may  be  continued
  unless  a  retroactive change is specifically required by the provisions
  of this code.