Ind. Code § 6-3.1-11-8

Sec. 8. As used in this chapter, "placed in service" means that property is placed in a condition or state of readiness and availability for a specifically assigned function. In the case of a plant comprised of a complex of buildings, the entire plant shall be considered to have been placed in service as of the date that a building was placed in service if the building has floor space that, when aggregated with the floor space of all buildings in the complex placed in service on earlier dates, exceeds fifty percent (50%) of the total floor space of all buildings in the complex.