Indiana Code Title 36. Local Government § 36-7-11.1-13

Sec. 13.  (a) Except as provided in section 13.1 of this chapter, any building, structure, or land use in existence at the time of the adoption of the historic preservation plan that is not in conformity to or within the zoning classification or restrictions or requirements or architectural standards of this plan, shall be considered to be a nonconforming use and may continue, but only so long as the owner or owners continuously maintain this use.

(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.