N.Y. Real Prop. Acts. Law § 401
The following interests shall be valued in the manner provided by this article: (a) an interest in real property dependent as to value upon the duration of one or more lives in being, whether such interest is present or future; and (b) a future interest preceded only by one or more interests described in clause (a); whenever 1. the owner of such interest is entitled to receive a sum in gross in satisfaction of, or in compensation for impairment of, his interest in real property which has been transformed into a fund by judicial action or proceeding; or 2. ownership of real property is divided into successive legal interests, including one or more interests dependent as to value upon the duration of one or more lives of persons in being, and the fraction of complete ownership belonging to each partial owner must be ascertained so as to permit an adjudication of the fraction of some new capital expenditure required either for the payment of a mortgage, special assessment or other lien upon such property, or for the satisfaction of an obligation imposed by law as an incident of ownership; or 3. such valuation is necessary for the final determination of some action or proceeding, other than an action or proceeding for which the insurance law, the workmen's compensation law or the tax law prescribes methods of valuation.
N.Y. Real Prop. Acts. Law § 401