The lawful use of a building existing at the time of the effective date of this chapter may be continued, although such use does not conform to the provisions hereof. If no structural alterations are made, a nonconforming use of a building may be changed to another nonconforming use of the same or a more restricted classification. Whenever a nonconforming use has been changed to a more restricted use or to a conforming use, such use shall not thereafter be changed to a less restricted one. Whenever the use of a building becomes nonconforming through a change in this chapter or district boundaries, such use may be continued, and if no structural alterations are made, it may be changed to another nonconforming use of the same or of a more restricted classification.

Whenever a nonconforming use of a building or structure or part thereof has been discontinued for a period of 12 consecutive months, or for a continuous period of 18 months if the building was originally designed and constructed for a nonresidential use, such discontinuance shall constitute and abandonment of such use. Where no enclosed building is involved, discontinuance of a nonconforming use for a period of six months shall constitute abandonment of such use, and any new use must be in conformity with the regulations of the district. However, if the Zoning Hearing Board determines the resumption of the discontinued use to be in harmony with the general intent of this chapter, it may grant a special exception permitting the resumption of the discontinued use.

No existing building or premises devoted to a use not permitted in the district in which such building or premises is located, except when required to do so by law, or permitted by special exception, shall be enlarged, extended, reconstructed or structurally altered, unless such use is changed to a use permitted in the district in which such building or premises is located.

Any building or structure containing a nonconforming use which is damaged by fire, flood, wind or other act of God or man to the extent of 75% or more of its fair sales value immediately prior to damage shall not be repaired or reconstructed except in conformity with the provisions of this chapter. In the event that the Zoning Officer's estimate of the extent of damage or fair sales value is not acceptable to the applicant for the building permit to repair or reconstruct such building or structure, the applicant may appeal to the Zoning Hearing Board.

No building or structure designed or intended to be utilized for a nonconforming use shall be constructed or allowed unless construction is already underway at the time of enactment or subsequent amendment of this chapter and is being diligently pursued so that such building or structure will be completed within 18 months from the date of the enactment or subsequent amendment of this chapter. All outstanding building permits for construction which do not meet these requirements are hereby rendered null and void.

The provisions of this Article shall not apply to any building or structure which is designated by the Zoning Hearing Board to be an historical landmark.

The Zoning Hearing Board may grant special exceptions permitting the reasonable extension of a nonconforming use or the reasonable enlargement or addition to a nonconforming building or structure, provided that it would be in conformity with the standards hereinafter set forth for granting special exceptions.