basis, measured by an estimate the tonnage of carbon dioxide emitted. (iii) The amount of carbon dioxide retained by the building which could otherwise be released into the atmosphere, taking into account building construction materials and processes and continuing use or disposal of carbon dioxide in connection with the use of the building. (iv) The climate in which the building is located. (C) Average sustainability The classes for which average sustainability scores are determined shall at least take into account the following distinguishing characteristics: (i) Residential and commercial buildings. (ii) Multi-family and single-family residential. (iii) The size, volume, and intended use of the building. (D) Updates The Secretary (in consultation with the Secretary of Energy) shall update the sustainability scoring and the sustainability score averages established under subparagraph (A) not less frequently than once every 5 calendar years. (E) Advisory board The Secretary shall establish a volunteer board that advises the Secretary on the sustainability score development and updates. Such board shall be appointed at the discretion of the Secretary and shall include experts in relevant fields, including energy, construction, transportation, agri­cul­ture, and labor. (c) Other definitions and special rules (1) Purchase price The term purchase price means so much of the adjusted basis of the property as is not attributable to land. (2) Qualifying building The term qualifying building or residence means, with respect to a taxpayer— (A) any dwelling unit first used as a residence by the taxpayer, or (B) any other building or structure of a character subject to the allowance for depreciation and first placed in service by the taxpayer. (3) Construction Any qualifying building or residence constructed by the taxpayer shall be treated as purchased by the taxpayer on the date the taxpayer first occupies the residence, or places such building in service, as the case may be. (4) Transfer of credit (A) In general If a