To avoid undue hardship, nothing in this chapter shall be deemed to require a change in the plans, construction or designated use of any building for which a valid building permit has been obtained, or on which actual construction was lawfully begun prior to the effective date of this chapter (Ordinance 76-31, passed June 21, 1976), and upon which actual building construction has been carried on diligently. "Actual construction" includes the placing of construction materials in a permanent position and fastened in a permanent manner. Where demolition or removal of an existing building has been substantially begun preparatory to rebuilding, such demolition or removal shall be deemed to be actual construction, provided that the work is carried out diligently. (Ord. 76-31. Passed 6-21-76.)