Except as provided in this Article, any nonconforming use of any structure or land existing on the effective date of this chapter may be continued.

In any district, whenever a nonconforming use of land, premises, building or structure has been discontinued for a period of one year, such nonconforming use shall not thereafter be reestablished, and all future use shall be in conformity with the provisions of this chapter.

Notwithstanding any other provisions of this chapter, any billboard, advertising structure or nonconforming sign in existence in any R-1, R-2 or R-3 District on the effective date of this chapter shall, at the expiration of three years from such date, become a prohibited and unlawful use and shall thereupon be discontinued; provided, however, that lawfully existing signs accessory to an institutional building or to a nonconforming business or industrial building shall not be subject to this section.

Once changed to a conforming use, no building or land shall be permitted to revert to a nonconforming use. A nonconforming use may be changed to a use of the same classification upon approval of the Board of Appeals or to a use of more restricted classification; and when so changed to a more restricted classification, such use thereafter shall not be changed to a less restricted classification.

A nonconforming use shall not be extended except within the same building or on the same lot, in the case of uses not located within buildings, which it partially occupied on the effective date of this chapter.

A building devoted to a nonconforming use may not be reconstructed or structurally altered during its life to an extent exceeding in aggregate cost 75% of the equalized assessed value (i.e., full value) of the building on the effective date of this chapter, unless said building is changed to a conforming use. No building damaged by fire or other causes to the extent of more than 75% of its equalized assessed value shall be repaired or rebuilt except in conformity with the regulations of this chapter, unless completely rebuilt on the original foundations within a period of two years from the date of such damage.

Whenever the boundaries of a district shall be changed so as to transfer an area from one district to another district of a different classification, or whenever the text of this chapter shall be changed with respect to the uses permitted in a district, the foregoing provisions shall also apply to any nonconforming uses existing therein.