N.Y. Real Property Tax Law § 421-PP
1.
2. Eligible newly-constructed or converted rental multiple dwellings in a designated benefit area shall be wholly exempt from taxation while under construction, subject to a maximum of three years. Such property shall then be exempt for an additional period of thirty years. Provided, however:
5. In the case of newly constructed property which is used partially as a rental multiple dwelling and partially for commercial or other purposes, the portion of the newly constructed property that is used as a rental multiple dwelling shall be eligible for the exemption authorized by this section if: