Nothing herein contained shall require any change in the plans, construction or designated use of a building actually under construction at the time of the passage of this ordinance and which entire building shall be complete within one year from the date of the passage of this ordinance. Nothing herein contained shall require any change in plan, construction or designated use of a building for which a building permit has been heretofore issued and which entire building shall be complete within six (6) months from the date of the passage of this ordinance. If any amendment to this ordinance is hereafter adopted changing the boundaries of districts, the provisions of this ordinance with regard to building, or premises existing or buildings under construction or building permits issued in the area affected by such amendment at the time of the passage of such amendment.