(a) On any building devoted in whole or in part to any nonconforming use, work may be done in any period of 12 consecutive months on ordinary repairs or on repair or replacement of nonbearing walls, fixtures, wiring or plumbing to an extent not exceeding ten percent of the replacement value of the building, provided that the cubic content of the building as it existed at the time of passage or amendment of the ordinance from which this section is derived shall not be increased and, provided further, that such repair or replacement shall not affect the assessed valuation-time allowance before termination setting the time limit for conformity, set forth in section 110-195(6).

(b) Nothing in this chapter shall be deemed to prevent the strengthening or restoring to a safe condition of any building or part thereof declared to be unsafe by an official charged with protecting the public safety, upon order of such official.