*2.1. The Green Energy Audit*

The energy diagnosis was introduced by Directive 2006/32/EC [37] and modified by Directive 2012/27/EU [38]: these directives request this procedure for all requalification actions. The interventions on historic building are usually considered voluntary: standard regulations for these cases are lacking [39]. The energy diagnosis general procedure was introduced by the UNI CEI EN 16247-1:2012 standard [15] that defines energy audits as a "systematic inspection and analysis of energy use and energy consumption of a site, building, system or organization with the objective of identifying energy flows and the potential for energy efficiency improvements and reporting them". The green energy audit retains the basic features of an energy audit but is aimed at a more important goal: improving the overall sustainability of the building. The main difference with the general energy audit's process is that during the analysis phase, only sustainability retrofits are evaluated. The audit is strictly related to environmental assessment protocols and the retro-commissioning process, presenting a systematic scheme to investigate the level of maintenance and operation of the systems in existing buildings, proposing operative interventions for improving the overall performance.

#### *2.2. The LEED O*+*M Rating System*

A different approach can be adopted in the management of the retrofit of an historical building based on LEED assessment scheme. Frequently, the complexity generated by cultural preservation and technical innovation and the necessity to find proofs of sustainability action through consistent documentation can discourage surveyors and technicians from pursuing the certification. Here, is considered the LEED O+M for buildings [37], which is normally intended for operative and management aspects for existing buildings undergoing limited retrofitting.

This protocol is subdivided into 20 mandatory prerequisites and 37 credits that indicate the points obtained from the characteristics of the structure and its management. The rating system organizes the prerequisites and credits into categories: Location and Transportation (LT), referring to the building site and the effect on commuting patterns; Sustainable Sites (SS), referring to environment surrounding the building and highlighting the relationship among services, ecosystems and buildings; Water Efficiency (WE), which considers water holistically, including indoor use, outdoor use, specialized uses, and metering, and recognizes the use of non-potable and alternative sources of water; Energy and Atmosphere (EA) focuses on the energy use reduction, renewable energy sources, and energy-efficient design strategies; Materials and Resources (MR), which considers the constant flow of products purchased and discarded to support building operations; Indoor Environmental Quality (EQ), which considers the satisfaction of occupants, the visual and thermal comfort, and the indoor air quality; Innovation (IN) identifies exemplary and innovative features or practices able to generate environmental benefits; and Regional Priority (RP), which identifies specific priorities according to the location and type of rating system.

The LEED performance credit system allocates points to each credit considering human benefits and the potential environmental impacts, so some categories are weighted according to the score of the associated credits, the relevance of the topic, and the intent described in the credit. As such, LEED O+M states that the categories EQ and EA are weighted higher than the total value of the other categories combined.

The structure of credits and prerequisites is organized in different sections: intent and requirements, behind the intent, step-by-step guidance, further explanation, required documentation and related credit tips, changes from LEED 2009, referenced standards, exemplary performance, and definitions [38]. It is a voluntary assessment tool that provides guideline to enhance the use of natural resources, to encourage restorative and regenerative policies, to maximize the positive and to minimize the negative environmental and human health consequences of the buildings sector, and to produce high quality indoor environments. LEED systems pursue sustainability goals by achieving mandatory prerequisites and choice credits. Four levels of sustainability are reachable according to the achieved points, platinum, gold, silver, and certified [23].
