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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]

• Quantitative assessment of the heat waves in different city zones. • Quantification of the heat waves impact on building energy performance. • Influence of heat waves on the indoor operative temperature. • Impact of the synergic effect of heat waves and urban heat island. Global and local climate change increases the occurrence and the magnitude of extreme phenomena, as urban heat island and heat waves. These phenomena seriously affect the quality of life in several aspects: society, health, environment; they also heavily affect the building sector, increasing the energy use for cooling and deteriorating the indoor thermal environment. This paper utilizes data from a continuous urban microclimatic monitoring over three years to quantify the impact of heat waves on the thermal quality of two reference residential buildings in the city of Rome, Italy. The synergic effect of heat waves with the urban heat island is also analysed. The observation period includes summers of 2015, 2016 and 2017. The buildings' response is analysed through numerical thermal analyses in transient regime, taking into account several variants: thermal insulation, mechanical cooling system and thermal free-floating conditions, with different night ventilation strategies. Results show that daily average temperature and urban heat island intensity increase by up to 4.3 °C and 1.5 °C respectively during the heat waves with respect to the rest of the summer. The building cooling energy use rises up 87% during heat wave periods, while average operative temperature in free-running buildings increments by up to 3.5 °C. Results also show the impressive combined impact of heat wave and heat island: triplication of cooling energy use in the worst case and increase of the average operative temperature above 5 °C. [ABSTRACT FROM AUTHOR]