Nothing contained in this chapter shall require any change in the plans, construction or designated use of a building complying with existing law, a permit for which shall have been duly issued and the construction of which shall have been started before the date of first publication of notice of the public hearing on this chapter and the ground-story framework of which, including the second tier of beams, shall have been completed within six (6) months of the date of the permit and which entire building shall have been completed in accordance with such filed plans within one (1) year from the date of passage of this chapter.