Section 269. Application of provisions

1. The provisions of sections two
  hundred and sixty-one,  two  hundred  and  sixty-two,  two  hundred  and
  sixty-three,  two hundred and sixty-five, two hundred and sixty-six, and
  two hundred and sixty-seven shall apply to all buildings  erected  after
  October  first,  nineteen  hundred and thirteen, and to all construction
  made after that date in buildings erected prior to that date. The  board
  shall  adopt  rules  affecting  construction  made before October first,
  nineteen  hundred  and  thirteen,  in  buildings  theretofore   erected,
  requiring  compliance with such of the requirements of said sections, or
  with such other or different requirements as  it  finds  reasonable  and
  adequate to protect persons employed in such buildings against fire.
    2.  Altered  buildings.  When  changes  are made to a building erected
  prior to October first, nineteen hundred thirteen, which are so material
  and extensive as to constitute  a  new  building,  such  building  shall
  comply  with the provisions of section two hundred seventy. However, the
  words material or extensive shall not apply if the structure is  altered
  by adding an extension horizontally in such manner as to increase any or
  all of its floor areas by not more than twenty-five per centum.