A use, building or structure lawfully in existence prior to the adoption of this chapter, which does not comply with the applicable use provisions of this chapter or any applicable amendment thereto, may be continued as provided herein. Nothing herein contained shall require any change in the plans, construction or designated use of a building complying with existing laws, a permit for which had been duly granted and the construction of which shall have been started before the date of adoption of this chapter or any applicable amendment thereto, and the ground story framework of which, including the second tier of beams, shall have been completed within six months of the date of the permit and which entire building shall have been completed, according to such plans as have been filed, within one year of the date of adoption of this chapter or any applicable amendment thereto.