Previously issued permits. 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 prior to the date of the 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, in accordance with such plans as have been filed, within one year from the date of passage of this chapter.