Buildings of a nonconforming use and buildings whose height, area or use exceeds or is different from that authorized for the zone in which located, when damaged by fire, explosion, act of God or the public enemy to such an extent that the estimated cost of the restoration does not exceed one-half (1/2) of the actual value of the building exclusive of foundations just prior to the damage, shall be considered as partially destroyed and may be restored.

Any nonconforming use lawfully existing at the time of passage of this chapter or thereafter may, subject to approval by the Mayor and Council, be changed to another nonconforming use which is no more harmful or objectionable provided that the building or premises involved shall be neither structurally altered nor enlarged unless the use of the altered or enlarged portion shall be changed to a use permitted in the zone in which it is located. No nonconforming use, if once changed to a use permitted in the zone in which it is located, shall be changed back to a nonconforming use.