Property is considered to be "substantially improved" if, during any 30-month period beginning after the property is acquired, additions to the basis of the property exceed an amount equal to the adjusted basis at the start of the 30-month period. This means that the improvements made to the property must increase its basis by more than the original adjusted basis of the property within that specified timeframe.
Sources:
§ 1.1400Z2(d)-1. Qualified opportunity funds and qualified opportunity zone businesses.
Rev. Rul. 2018-29
§ 1.168(b)-1. Definitions.
Qualified Improvement Property and Bonus Depreciation
§ 1250. Gain from dispositions of certain depreciable realty
§ 168. Accelerated cost recovery system
