1. Short title This Act may be cited as the Building Efficiently Act of 2018 . 2. Expansion of new energy efficient home credit (a) In general Paragraph (2) of section 45L(a) of the Internal Revenue Code of 1986 is amended by striking and at the end of subparagraph (A), by striking the period at the end of subparagraph (B) and inserting , and , and by adding at the end the following: (C) in lieu of subparagraphs (A) and (B), in the case of qualified new energy efficient home that is a qualified energy efficient residential rental property, 3.3 percent of the cost of construction of such property, reduced by any expenditure not taken into account under this section by reason of subsection (f). . (b) Qualified energy efficient residential rental property defined Subsection (b) of section 45L of such Code is amended by adding at the end the following: (5) Qualified energy efficient residential rental property (A) In general The term qualified energy efficient residential real property means a building which is residential rental property which is described in subparagraph (B), (C), or (D). (B) New or reconstructed building A building is described in this subparagraph if— (i) the certification requirements of subparagraph (E) with respect to the building are met, (ii) the original use of which commences with the taxpayer, and (iii) the building is placed in service after the date of the enactment of the Building Efficiently Act of 2018 . (C) Improvements to existing building A building is described in this subparagraph if, only after improvements are made to the building— (i) the certification requirements of subparagraph (E) with respect to the building are met, (ii) the original use of the improved building commences with the taxpayer, (iii) the improved building is placed in service after the date of the enactment of the Building Efficiently Act of 2018 , and (iv) the taxpayer elects to the application of this paragraph with respect to the building. (D) Buildings acquired by purchase A building is described in