Any lawful nonconforming structure may be extended, enlarged, reconstructed, or structurally altered, provided that said extension, enlargement, reconstruction, movement or alteration complies with the setback and building requirements of the specific zoning district. However, the nonconforming feature of said structure shall not be allowed to become more nonconforming by being extended, enlarged, reconstructed, moved, or structurally altered except under one or more of the following fact situations:
(a) As when required to do so by law or order.
(b) To comply with the provisions of this chapter.
(c) With the approval of a conditional use permit under the procedures of Article
V of this chapter for the purpose of making required alterations to maintain the structural integrity of the building.
(d) With the approval of a variance by the Zoning Board of Appeals.