cost-effective
(2) The term “cost-effective” means, with respect to energy efficiency improvements to a residential building, improvements that result in the total present value cost of the improvements (including any maintenance and repair expenses) being less than the total present value of the energy saved over the useful life of the improvement, when 100 percent of the cost of improvements is added to the base loan. For purposes of this paragraph, savings and cost-effectiveness shall be determined pursuant to a home energy rating report sufficient for purposes of the Federal National Mortgage Association and the Federal Home Loan Mortgage Corporation, or by other technically accurate methods.