Abandonment. The change of a nonconforming use to a more restricted, or conforming use for any period of time shall be considered an abandonment thereof, and such nonconforming use shall not thereafter be revived.

Partial Destruction. When 80% or more of the existing area of a nonconforming structure is destroyed by fire or other casualty or an act of God, the use of such structure as a nonconforming use shall thereafter be terminated.

Nonconforming Buildings Lawfully Under Construction. Any nonconforming building or structure lawfully under construction on the effective date of this chapter, pursuant to plans filed with the Construction Official and approved by him and all other municipal boards and agencies as required under law, may be completed and may be used for the nonconforming use for which it was designed, to the same extent as if such building had been completed and been in use at the effective date of this chapter, provided that such building or structure shall be completed within one year after the effective date thereof.

Nonconforming Billboards. A nonconforming billboard which is damaged by elements to such an extent that its supporting members are broken shall be deemed to have been destroyed and shall not be reconstructed.