(A) Normal maintenance of a building or other structure containing a non-conforming use is permitted, including necessary non-structural repairs and incidental alterations which do not extend or intensify the non-conforming use.
(B) No structural alteration shall be made in a building or other structure containing a non-conforming use, except in the following situations:
(1) When the alteration is required by law;
(2) When the alteration will actually result in elimination of the non-conforming use; and
(3) When a building is in a residential district containing residential non-conforming uses, it may be altered in any way to improved livability, provided no structural alterations shall be made which would increase the number of dwelling units or the bulk of the building.