Furthermore, the lack of confidence of building industry and building owners in the real energy performance of nZEBs and the concrete risks associated to new technologies seem to represent one of the keypoints the resolution of which could possibly solve the problem related to the high investments required in the process. In this context, the RePublic_ZEB proposal is focused on economically sustainable strategies and policies aimed at enforcing the refurbishment of the public building stock towards nZEB levels, according to EU 20/20/20 target. Thus the main objectives are to encourage the South-Eastern European countries to promote on the market a set of concrete technical solutions for the refurbishment of their public building stock towards the nearly zero energy target by increasing the involved key actors' confidence in nZEB, taking this way tangible steps to accelerate the renovation process and boost a real market demand to such buildings.

In order to achieve the above mentioned goals, the addressed key actors are meant to be builders and public building owners, policy developers (authorities), building technology industries and national professionals associations referred to the building industry (as architects and engineers). The thesis mainly concerned Work Package n° 3 (Assessment of the status quo and analysis of opportunities for refurbishing public buildings towards nZEB) and Work Package n° 4 (Costs/ benefits analysis of the "packages of measures" for the refurbishment towards nZEB): these were also the steps taken in our work, applying cost optimality on the office case study.

Within the first step, the energy efficiency measures to be applied through deep refurbishment interventions on offices were detailed. The interventions concern the building envelope, HVAC, DHW and lighting systems, including technologies based on the usage of RES. This stage was aimed to define a set of the most suitable building technologies (Energy Efficiency Measures) available on the italian market to reach the nZEB target for the public building stock. Local installers, manufacturers and technicians were involved in the market survey. We committed to being as precise as possible regarding the costs of the several interventions, going beyond the Piedmont Price List, our purpose was not to underestimate the evaluations, trying to provide costs and technical data as close as possible to reality, assuming the real implementation of such a project.

In the following phase, corresponding to the WP4, the most suitable building technologies and technical systems were combined into packages of measures for the cost optimal energy and economic analysis. The aim of this step was to provide quantitative results in terms of saving energy and corresponding cost benefits that, in case of a real refurbishment, could increase builders' confidence in nZEB projects.

For the application of this methodology, an Excel format calculation tool was developed by the DENERG, it consists in a series of interconnected sheets able to provide, for each case study considered, the best cost-benefit technology solution aimed at reducing energy consumption, both for new buildings and existing buildings undergoing total renovation. The energy assessment was conducted using a quasi-stationary methodology, in accordance with technical specifications UNI/TS 11300-1/4, in order to predict global energy consumption for individual buildings; the economic assessment was conducted in accordance with standard UNI EN 15459 with the aim to predict the overall cost in a context of new construction or total renovation.

In conclusion, it can be said that, as the nZEB is not yet considered cost-efficient, cost optimal and nZEB requirements still have to be reconciled so that a smooth transaction from cost optimal requirements to nearly zero energy buildings could be guaranteed. This will require significant policy interventions, including increased support for research, development, deployment and demonstration of advanced building technologies. Such european projects are essential for policy makers as they can provide them tools to critically analyze the incentive system of our country, to identify any inconsistencies introduced in the recent past and to search for the opportunities offered by new technologies, in order to optimize the efforts. This is even more important for Italian public existing buildings, for which nZEB renovations requirements have just been introduced and common practices still need to be assessed.