(4) Property which is substantially improved For purposes of this subsection— (A) In general The term “separate improvement” means each improvement added during the 36–month period ending on the last day of any taxable year to the capital account for the property, but only if the sum of the amounts added to such account during such period exceeds the greatest of— (i) 25 percent of the adjusted basis of the property, (ii) 10 percent of the adjusted basis of the property, determined without regard to the adjustments provided in paragraphs (2) and (3) of section 1016(a), or (iii) $5,000. For purposes of clauses (i) and (ii), the adjusted basis of the property shall be determined as of the beginning of the first day of such 36–month period, or of the holding period of the property (within the meaning of subsection (e)), whichever is the later. (B) Exception Improvements in any taxable year shall be taken into account for purposes of subparagraph (A) only if the sum of the amounts added to the capital account for the property for such taxable year exceeds the greater of— (i) $2,000, or (ii) one percent of the adjusted basis referred to in subparagraph (A)(ii), determined, however, as of the beginning of such taxable year. For purposes of this section, if the amount added to the capital account for any separate improvement does not exceed the greater of clause (i) or (ii), such improvement shall be treated as placed in service on the first day, of a calendar month, which is closest to the middle of the taxable year. (C) Improvement The term “improvement” means, in the case of any section 1250 property, any addition to capital account for such property after the initial acquisition or after completion of the property.