(1) Such structure may not be enlarged or altered in a way which increases its nonconformity, but any structure or portion thereof may be altered to decrease its nonconformity.

(2) Should such structure be destroyed by any means to an extent of more than 50 percent of its fair market value at time of destruction, it shall not be reconstructed, except in conformity with this chapter.

(3) Should such structure be moved for any reason for any distance whatever, it shall thereafter conform to the regulations of the district in which it is located after it is moved.

(4) Where a lawful dwelling structure, located on a single lot of record, exists at the effective date of adoption or amendment of the ordinance from which this section is derived that could not be built under this chapter, such structure may be repaired, enlarged, extended, rebuilt, reconstructed or structurally altered, provided that setback dimensions, maximum lot coverage, building setback lines and other requirements of the additional structure conform to the regulations for the district in which such lot is located. Any additional construction to an existing structure that encroaches on setback requirements must conform to the setback requirements of the zoning district. Any legally established encroachment on setback requirements may be repaired, rebuilt, reconstructed or structurally altered, but not enlarged or extended, provided the encroaching portion of the structure is an integral part of the structure.