Any building or land devoted to a use not permitted by this chapter in a Residential District in which such building or land is located, except when required by law, shall not on one or more cumulative occasions be substantially enlarged, extended, constructed, reconstructed, substituted or structurally altered, at a value of greater than 50 percent of the fair market value of the existing building or land, unless the use thereof is changed to a use permitted in the district in which such building, structure or premises is located, except as follows:

1.   Substitution. If no substantial structural alterations are made, as specified above, a nonconforming use of a building or structure may be changed to another nonconforming use of the same or a more restricted classification. Whenever a nonconforming use has been changed to more restricted use or to a conforming use, such shall not thereafter be changed to a less restricted use.

2.   Discontinuance. In the event that a nonconforming use of any building, structure or land is discontinued for a period of one year, the use of the same shall conform thereafter to the uses permitted in the district in which it is located. The use of land upon which no building or structure is erected or constructed which does not conform to the provisions of this chapter and the use of land upon which no building is erected or constructed which becomes nonconforming by reason of a subsequent change in this chapter shall be discontinued within six months from the date of the change.

3.   Replacing Damaged Buildings. Any nonconforming building or structure damaged to an extent of 50 percent or more of its fair market value (prior to destruction or damage by fire, flood, explosion, war, riot, or Act of God), shall not be restored or reconstructed and used as before this chapter unless brought into conformity with the provisions of this chapter.