a dwelling unit— (A) located in the United States, (B) owned and used by the taxpayer as the taxpayer's principal residence (within the meaning of section 121), and (C) which is certified to have— (i) a projected annual level of energy consumption after the energy efficiency improvements have been placed in service that is less than the annual level of energy consumption prior to the energy efficiency improvements being placed in service, and (ii) an efficiency ratio of not less than 20 percent. (2) Energy efficiency improvements (A) In general The term energy efficiency improvements means any property installed on or in a dwelling unit which has been certified to reduce the level of energy consumption for such unit, provided that— (i) the original use of such property commences with the taxpayer, and (ii) such property reasonably can be expected to remain in use for at least 5 years. (B) Amounts paid or incurred for energy efficiency improvements For purposes of subsection (a)(2), the amount paid or incurred by the taxpayer— (i) shall include expenditures for design and for labor costs properly allocable to the onsite preparation, assembly, or original installation of the property, and (ii) shall not include any expenditures related to expansion of the building floor area. (d) Special rules For purposes of this section: (1) Tenant-stockholder in cooperative housing corporation In the case of an individual who is a tenant-stockholder (as defined in section 216) in a cooperative housing corporation (as defined in such section), such individual shall be treated as having made his tenant-stockholder's proportionate share (as defined in section 216(b)(3)) of any expenditures for energy efficiency improvements of such corporation. (2) Condominiums (A) In general In the case of an individual who is a member of a condominium management association with respect to a condominium which the individual owns, such individual shall be treated as having made the individual's proportionate share of any expenditures for energy