The restoration and resumption of the former use of a nonconforming building that is damaged or partially destroyed by fire, explosion, Act of God or the public enemy to the extent of seventy-five (75) percent or less shall be permitted, provided that such restoration is permitted by the building code of the county and is started within one year after such damage and diligently prosecuted to completion. A nonconforming building that is completely destroyed, or damaged or partially destroyed to a greater extent than above specified, shall not thereafter be restored, except in full conformity with all the regulations of this title, except that dwellings in the A district that are nonconforming solely because they were not subject to site development review pursuant to Section 17.06.090 of this title, may be restored without regard to the extent of such damage. The proportion of damage or partial destruction shall be based upon the ratio of the estimated cost of restoring the building to its prior condition to the estimated cost of duplicating the entire structure as it existed prior thereto. Estimates for this purpose shall be made by the building official. (Prior gen. code § 8-62.7)