Nothing herein contained shall require any changes in the plans, construction or designated use of a building for which a building permit has been heretofore issued of plans for which are on file with the Construction Code Official at the time of the passage of this chapter and any amendments thereof, and the construction of which in either case, shall have been diligently prosecuted within a year of the date of such permits and the ground story framework of which, including the second tier of beams, shall be completed within such year and which entire building shall have been completed according to such plans as files within two years from the date of the passage of this chapter and any amendments thereof.