Continuance. Nothing contained in this chapter shall require any change in the plans, construction or designated use of a building for which a valid construction permit has been heretofore issued or plans for which are on file with the Construction Official at the time of the effective date of this chapter, and a permit for the erection of which is issued within 30 days after the effective date of this chapter and the construction of which, in either case, shall have been diligently prosecuted within six months of the date of such permit, and the ground storm framework of which, including the second tier of beams shall be completed within such six months, and which entire building shall have been completed according to such plans as filed within one year from the date of the effective date of this chapter.