The lawful use of a building or premises existing at the time of the adoption or amendment of the village zoning regulations may be continued although such use does not conform with the provisions of said zoning regulations. Such nonconforming use may not be extended. The total structural repairs or alterations in such a nonconforming building shall not, during its life, exceed fifty percent (50%) of the assessed value of the building unless permanently changed to a conforming use. If such nonconforming use is discontinued for a period of twelve (12) months, any future use of the building and premises shall conform to this title. (1968 Code ch. 12)