Continuance. Except as otherwise provided herein, nonconforming uses or structures which lawfully existed at the time of passage of this chapter may be continued even though such uses or structures do not comply with the regulations of this chapter; provided, however, that:
1. A nonconforming use shall not be expanded or changed to another nonconforming use.
2. Any addition to an existing nonconforming building may be constructed to continue the existing building setback, but shall not be permitted to encroach further into the required setback than the existing structure. Furthermore, any vertical addition may not exceed eighty (80%) percent of the original building footprint.
3. Abandonment. A nonconforming use that has been abandoned shall not thereafter be reinstated. A nonconforming use shall be adjudged to have been abandoned:
(a) When it is changed to a conforming use.
(b) In cases where such nonconforming use is a building or structure designed for such use, when it has been voluntarily discontinued for a period of twenty-four (24) consecutive months.
(c) In cases where such nonconforming use is of a building or structure not designed for such use or is of a lot or land whereon there is no consequential building or structure devoted to such use, when it has been voluntarily discontinued for a period of twelve (12) consecutive months.