Nothing contained in this title shall require any change in the plans, construction or designated use of a building for which a building permit has heretofore been issued and upon which actual construction has begun. “Actual construction” means the actual placing of construction materials in their permanent position fastened in a permanent manner, except that where a basement is being excavated such excavating shall be deemed to be actual construction or where demolishing or removal of an existing building or structure has been begun preparatory to rebuilding, such demolition or removal shall be deemed to be actual construction, providing in all cases that actual construction work be diligently carried on until the completion of the building or structure involved. In no case shall actual construction exceed the two-year time limit of the original building permit. (Ord. 409, eff. 7/5/73; Prior code § 86104)