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, provided that the cubic content of the building as it existed on August 11, 1972, or the date of any amendment hereto, shall not be increased.

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 any official charged with protecting the public safety, upon order of such official.