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• Identification of solution sets to reduce construction costs in nearly zero energy houses. • 15% maximum reduction of energy related construction cost in Continental Italy. • 26% maximum reduction of energy related construction cost in Mediterranean Italy. • Net present values up to 163 €/m2 after 50 years building lifetime. Concerning Nearly Zero Energy Buildings, it is important to guarantee energy efficiency, thermal comfort and indoor environmental quality, while keeping construction and operational costs low. In this framework, this paper explores the efficacy of applying different scenarios, for reducing construction costs of new nearly zero energy multi-family houses in a life cycle perspective. Conversely to the standard cost-optimal approach, a real Italian case study building was chosen. Alternative and unconventional combinations of solutions for envelope and technical systems were adopted. Calculations were performed in two Italian cities (Rome and Turin). Three types of analysis were developed thermal comfort, energy performance and financial calculation. Results of the thermal analysis show that the installation of active cooling to prevent summer overheating can be avoided by applying low-cost passive strategies. All the proposed low-cost scenarios (4 alternative scenarios in Rome and 5 in Turin) reached the highest grade of energy performance, with a reduction of the non-renewable primary energy consumption up to 46% compared to the base case in Rome and 18% in Turin. From the economic perspective, all the scenarios in the two climate zones allow both reductions in the construction costs, up to 26% in Rome and 15% in Turin, and a Net Present Value after 50 years up to 163 €/m2 in Rome and 158 €/m2 in Turin. [ABSTRACT FROM AUTHOR]

• The annual net energy saving of switching cool roofs is assessed via dynamic models. • Thermochromic cool roofs provide savings up to 19% compared to conventional roofs. • Thermochromic cool roofs provide savings up to 8% compared to cool roofs. • Limited switching magnitude comes with limited energy savings or even penalties. Cool materials are a well established solution to mitigate urban overheating. Notwithstanding, their net energy and cost impact might turn negative in year-round assessments, owing to space heating penalties. Thermochromic materials, that are able to switch from a prevalent absorbing to a prevalent reflective behaviour, may overcome this problem. Several studies at the material level show advantages and limits of the technology, however no marketable solution exists yet. This study aims at quantifying the energy saving potential of switching cool roofs to optimize the thermal response of residential buildings in the Mediterranean Basin. The task is performed by simulation in transient regime, drawing on different material modelling approaches. The analysis is carried out in three cities: Barcelona, Palermo and Cairo, representative of different areas of the Basin. Several scenarios are considered, different in terms of building insulation, transition temperature and switching magnitude. Thermochromic materials exhibit potential annual energy savings up to 8.5% and 19% with respect to cool and conventional roofs, respectively, when the solar reflectance switches from 0.15 to 0.75. Smaller annual energy savings are achieved as the switching magnitude is decreased. Due to several factors, thermochromic cool roof can also lead to annual energy penalties compared to static roofs. Further modelling and experimental efforts are needed to better predict the response of the material during the transition phase and refine the optimization process. [ABSTRACT FROM AUTHOR]