Buildings energy retrofit: components service life impact on the costs-benefits analysis

Life Cycle Costing (LCC) procedures can be used in building renovation interventions for the evaluation of the costs and benefits of different design solutions during the building life-cycle. LCC methods are commonly applied to energy retrofit measures according to standard EN 15459. However, these procedures can provide significantly different results in relation to the methods used to characterise the economic and technical parameters used as data inputs in the calculation. Several authors highlighted how the uncertainties related to the quantification of the initial investment and maintenance costs, to the economic scenarios (inflation and interest rates), to the costs of energy and labour and to the "service life" of the components strongly affect the results. The assumption of different inputs data sets can then result in significantly different results. Hence, prior to the application of LCC procedures, performing sensitivity analysis can be useful for understanding if and how each of these parameters can influence the results. This study analyses the influence that different assumptions on the building components service life have on the economic benefits due to energy retrofit interventions. In particular, through a specifically developed probabilistic procedure, we evaluated the influence on the Global Costs of different assumptions on the probability distributions of the service life of internal thermal insulation systems. The results show that the uncertainty on the Global Costs is primarily influenced by the variance of the economic parameters (interest rates and growth rate of the gross domestic product). However, within a given macro-economic scenario, the service life of the building components is an important technical parameter, able to strongly influence the variance of the final results and therefore the uncertainty about future benefits.