Where a lawful structure exists at the effective date of adoption or amendment of the ordinance codified in this chapter that could not be built under the terms of this chapter by reason of restrictions on area, lot coverage, height, yards, or other characteristics of the structure or its location on the lot, such structure may be continued for as long as it remains otherwise lawful, subject to the following provisions:

1.   No such structure may be enlarged or altered in a way which increases its nonconformity.

2.   Should such structure be destroyed by any means to an extent of more than 50 percent of its replacement cost at the time of destruction, it shall not be reconstructed except in conformity with the provisions of this chapter.