Nothing herein contained shall require any change in the plans, construction or designated use of a building actually under construction or designated use of a building actually under construction within the City on the effective date of this ordinance and which entire building shall be completed within one (1) year from the effective date of this ordinance or which building shall be maintained under continuous construction even though not completed within one (1) year. 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 while such permit is valid and provided the building shall have been started within six (6) months of the date of issuance of the permit and which building shall be completed within one (1) year from the effective date of this ordinance or which building shall be maintained under continuous construction even though not completed within one (1) year.