Except as provided in §§ 139-49 and 139-50 of this article, any use of land or a building or structure or part thereof legally existing at the time that this chapter or part thereof or any amendment hereto becomes effective may be continued, subject to the provisions of §§ 139-51, 139-52, and 139-53 of this article, although such building or structure or use does not conform to the provisions of the district in which it is situated.

When a nonconforming use has been discontinued or abandoned for a period of one year or longer, it shall not thereafter be reestablished, and the future use shall be in conformity with the provisions of this chapter. All farms are exempt from the provisions of this section.

Notwithstanding any other provision of this chapter, any automobile or other junkyard or any billboard or nonconforming sign or advertising device in existence in a residence district at the time of the adoption of this chapter or an amendment hereto shall be discontinued within one year from the date of such adoption or amendment.

A nonconforming use may be changed to another nonconforming use of the same or higher classification according to the provisions of this chapter, and when so changed such use shall not thereafter be changed to a nonconforming use of a lower classification. The classifications of uses in ascending order are C-M, C-1, R-MHP, R-1, R-H and A (AR, for future use).

A nonconforming use is hereby required to be maintained in such condition as will not constitute a danger to the safety, health or general welfare of the public and as not to constitute a nuisance beyond that generally inherent in such a nonconforming use in the district in which it is situated. Proposed alterations and extensions of the nonconforming use shall be reviewed by the Zoning Board of Appeals to ensure that such alteration or extension shall not tend to increase the inherent nuisance and that such alteration or extension shall not violate any provisions of this chapter regarding yards, lot area or lot coverage for the district in which it is situated or to increase any existing violation of such provisions.

Nothing herein shall prevent the substantial restoration within one year and continued use of a nonconforming building or structure damaged by fire, flood, earthquake, act of God or act of the public enemy, provided that such restoration shall comply with the provisions of § 139-52 of this article. All farms are exempt from the provisions of this section.