Buildings energy retrofit : dealing with uncertainty

Over the span of the past decade, the interest in issues related to building energy efficiency has been ever growing. Consequently, an increasing amount of studies has focused on the economic viability of energy retrofit measures. Despite all these research efforts, the results are still uncertain and conflicting. Nonetheless, such studies have brought out the main variables affecting the economic feasibility of interventions improving building energy performance: savings-investment ratio, cost-effectiveness of energy supply, energy price trends. The aim of this paper is to investigate the relevance of an often disregarded aspect: the rate of time preference as an expression of households’ behaviours, that is to say, the discount rate adopted within several valuation approaches, which are based on discounted cash flow. A case study analysis is performed on a refurbishment project. It concerns a public housing estate, built during the seventies, located in the suburbs of Bologna. A number of retrofit alternatives are examined, by resorting to different judgement criteria, particularly the Net Present Value. It is shown that uncertain results may occur repeatedly, more frequently than literature has evi-denced. Moreover, unclear outcomes closely correlate to the discount rate level, which may lead to conflicting options; therefore, it is hard to unequivocally identify the alternative characterized by the highest NPV.