Ind. Code § 36-7-11.1-13
(b) Except as provided in section 13.1 of this chapter, in addition to the requirements pertaining to certificates of appropriateness, the ownership of a nonconforming use is subject to the additional restriction that a nonconforming use may not be reconstructed or structurally altered to an extent exceeding in aggregate cost fifty percent (50%) of the market value thereof unless the structure is changed to a conforming use.
As added by Acts 1982, P.L.77, SEC.6. Amended by P.L.113-1998, SEC.2.