A variance to the substantial improvement requirements of this section is authorized provided that the repair or rehabilitation of a historic structure is completed according to N.J.A.C. 5:23-6.33, Section 1612 of the International Building Code and R322 of the International Residential Code, the repair or rehabilitation will not preclude the structure's continued designation as a historic structure, the structure meets the definition of the historic structure as described by this section, and the variance is the minimum necessary to preserve the historic character and design of the structure.