No existing building or structure devoted to a use not permitted by this Chapter in the district in which it is located shall be enlarged, extended, constructed, reconstructed, moved or altered except in changing the use of such building or structure to a use permitted in the district in which it is located. On a structure devoted to a non-conforming use, work may be done in any period of twelve (12) consecutive months on ordinary repairs or replacement of non-bearing walls, fixtures, wiring or plumbing to an extent not to exceed ten percent (10%) of the then current replacement value of the structure, provided that the volume of such building or the size of such structure as it existed at the effective date of adoption or amendment of this Chapter shall not be increased.