ENERGY RENOVATION STRATEGIES FOR HISTORICAL BUILDINGS: COST-OPTIMAL ANALYSIS FOR A CASE STUDY IN CATANIA (SICILY)

Historical buildings are usually excluded from the obligation of complying with specific energy standards, and they must follow the EPBD requirements only limited to energy certification and operation, maintenance and inspection of technical systems. In fact, the energy renovation of this kind of buildings is a very complex matter that leads to a number of questions concerning cultural, conservation, valorisation and economic aspects. This paper tries to answer these questions, starting from a typical building in the historical centre of Catania (Sicily), which nowadays hosts a public office. Firstly, the energy needs of the building, which is already equipped with an efficient heat pump system, were calculated. Then, different retrofit packages were selected, analysed and compared in terms of energy performance and cost of intervention. These packages include different insulation options for walls (internal aerogel boards, internal calcium silicate boards, external and internal insulation plaster), roof (under-tile thermal insulation system) and windows (integration of double-glazing). The energy needs of the building after the different retrofit actions have been calculated and the intervention costs have been assessed, considering real market prices. An economic analysis has been conducted applying the cost optimal methodology: this identifies the energy performance level that leads to the lowest cost during the estimated economic life cycle of the building, and allows choosing among different retrofit packages, considering their efficiency in terms of energy savings and costs. In parallel, the discounted payback time (PBT) has been also calculated for the same retrofit packages. Even if the highest energy savings have been achieved with the internal application of aerogel boards, this intervention shows the longest PBT and leads to the highest global costs during the economic life cycle of the building, because of the high prices of aerogel. The shortest PBT and the lowest global costs are achievable by applying internal calcium silicate boards. This study also highlights that current Italian policies do not adequately match the requirements of historic buildings. Indeed, since retrofit measures have to preserve the historic and cultural value of this kind of edifices, the level of transmittance requested to benefit from fiscal and financial incentives are often not technically feasible.