The EU Member States are being involved to develop long-term strategies and to promote investments aimed at improving the energy efficiency of the building stock, at increasing the use of Renewable Energy Sources (RES) and at growing the number of Nearly Zero-Energy Buildings (NZEBs). The aim of this article is to investigate energy and economic implications related to the exploitation of RES in the transformation of an Italian social housing building-type into a NZEB. The research is based on a detailed energy audit procedure that includes cost-optimal assessment and compliance check with the legal requirements. A parametric analysis was performed to find out the technical building system configurations that verify the minimum share of RES established by the Italian regulations, and at the same time to assess global cost and payback period. The intersection between legal compliancy and cost-effectiveness narrows the field of applicable RES technologies that are limited to electric heat pump for heating and cooling coupled with PV system, and low size solar collectors coupled with low temperature generator for domestic hot water. Improvements in the energy policy are necessary to guarantee the best trade-off between RES exploitation, energy efficiency and costs, as to preserve market equilibrium. (c) 2020 Elsevier Ltd. All rights reserved.