this subclause is met if such amount is not less than 20 percent of the adjusted basis of the building (determined as of the 1st day of such period and without regard to paragraphs (2) and (3) of section 1016(a)). (II) The requirement of this subclause is met if the qualified basis attributable to such amount, when divided by the number of middle-income units in the building, is equal to or greater than the dollar amount in effect under section 42(e)(3)(A)(ii)(II) for the calendar year in which such expenditures are treated as placed in service under paragraph (4). (B) Date of determination The determination under subparagraph (A) shall be made as of the close of the 1st taxable year in the credit period with respect to such expenditures. (4) Special rules For purposes of applying this section with respect to expenditures which are treated as a separate building by reason of this subsection— (A) such expenditures shall be treated as placed in service at the close of the 24-month period referred to in paragraph (3)(A), and (B) the applicable fraction under subsection (c)(1) shall be the applicable fraction for the building (without regard to paragraph (1)) with respect to which the expenditures were incurred. Nothing in subsection (d)(2) shall prevent a credit from being allowed by reason of this subsection. (5) No double counting Rehabilitation expenditures may, at the election of the taxpayer, be taken into account under this subsection or subsection (d)(2)(A)(i) but not under both such subsections. (6) Regulations to apply subsection with respect to group of units in building The Secretary may prescribe regulations, consistent with the purposes of this subsection, treating a group of units with respect to which rehabilitation expenditures are incurred as a separate new building. (f) Definition and special rules relating to credit period (1) Credit period defined For purposes of this section, the term credit period means, with respect to any building, the period of 15 taxable years beginning with— (A) the