The European energy policies about climate and energy packages, known as the “20-20-20” targets, define ambitious, but achievable, national energy requirements. The Directive 2010/31/UE, the “Commission delegated regulation (EU)” n.244/2012 and “Guidelines accompanying Commission Delegated Regulation (EU) n.244/2012” 2012/C 115/01 define a comparative methodology framework for calculating cost-optimal levels of minimum energy performance requirements for buildings and building elements to apply at “Reference Building” for EU State Member. The aim the of Cost-Optimal Level is to supply EU Member State in order to define national energy requirements levels, economically feasible, which could reduce energy consumption until 2020. Follow the Italian and regional laws, the UNITS 11300 standard procedures allow calculating energy building performance simulation (EPBS), and energy costs depend on these conditions. The Reference building could be ‘calibrated’ in order to compare it EPBS with real energy consumption. However, the cost of improvements depends on local variable ad contract tender. In this paper a case study application of Cost-Optimal Level, following EU procedure, is described in Italian context, in order to highlight the real and actual difficulties to apply EU rules.