A variance to the substantial improvement requirements of this Section 21-8A 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 21-8A, and the variance is the minimum necessary to preserve the historic character and design of the structure.