(1) The provisions of section 15-1-465, so far as applicable and excepting those provisions concerning costs of, or special taxes or assessments for, improvements to property, shall govern the apportionment of expenses between tenants and remaindermen where no trust has been created; except that such apportionment shall be subject to any legal agreement of the parties or any specific direction of the taxing or other statutes. If either tenant or remainderman has incurred an expense for the benefit of his or her own estate and without the consent or agreement of the other, he or she shall pay such expense in full.

(2) Subject to the exceptions described in subsection (1) of this section, the cost of, or special taxes or assessments for, an improvement representing an addition of value to property forming part of the principal shall be paid by the tenant, if such improvement cannot reasonably be expected to outlast the estate of the tenant. In all other cases, a portion thereof only shall be paid by the tenant, while the remainder shall be paid by the remainderman. Such portion shall be ascertained by taking that percentage of the total that is found by dividing the present value of the tenant's estate by the present value of an estate of the same form as that of the tenant; except that, it is limited for a period corresponding to the reasonably expected duration of the improvement. The computation of present values of the estates shall be made on the expectancy basis set forth in the American experience tables of mortality, and no other evidence of duration or expectancy shall be considered.