**1. Introduction**

According to the United Nations previsions [1], in 2050, most people will live in cities or urban centers; therefore, it is increasingly vital to work toward a more sustainable urban environment and to guarantee adequate public services realizing greener cities [2]. In European countries like Italy, this presents a significant challenge due to the historical context and important cultural heritage witnesses.

Historical buildings express the cultural identity of European countries, characterize cities, and provide continuity of the connection from our past to our future [3]. Historic centers have the potential to valorize different cultures and to attract financial capital, real estate investments, and building renovation projects, so it is necessary to think about how to coordinate the continuous intervention and management of historic centers to increase citizen and tourist attendance and improve relevant economic and cultural activities. A main goal of managing these centers is to detect and promote new tools for the sustainable management of historic centers. This management would enhance the attractiveness of city centers and their surroundings, increasing their suitability for both citizens and tourists [4]. National authorities are committed to valorization policies for the buildings of their historical heritage. Energy retrofitting could provide an effective strategy to protect the cultural heritage through operational costs reduction and environmental quality improvement [5]. Unfortunately, the evaluation of environmental and energy performance of historical buildings is complex and requires dedicated tools, sophisticated diagnostic procedures, and an interdisciplinary approach [6–8]. The energy requalification process must not work against the conservation necessities; it has to be an instrument of protection [9,10].

Energy and environmental diagnosis should be integrated for better identifying inefficiencies and wastefulness and to define the most appropriate retrofit measures [11]. In this context, two tools exist: the green energy audit that integrates the methodologies for evaluating energy performance (energy audit) and environmental impacts (green assessment) tools to guide green retrofits [12], and the green assessment protocols [13]. The most common of these analysis tools are multi-criteria, and evaluations are based on comparisons with real or reference performance [14,15]. Developed by the United States Green Building Council (USGBC) in 1998, currently Leadership in Energy and Environmental Design (LEED), represents the most influential and widespread rating system [16]. This certification system has been set for all types of buildings and proposes different protocols according to the typology, from home to hospital, from data center to school. The USGBC database reports that more than 100,000 projects are listed or certified by LEED, making it the most used certification system in the world [17].

The application of sustainability assessment protocols to the energy retrofit of historic buildings faces various difficulties [18,19]. Even if sustainability aspects were originally integrated into historical buildings, some rehabilitation processes ignore some of the sustainability aspects, and specific categories and criteria of rating systems, such as indoor environmental quality, conservation of materials and resources, and sustainability in the site management, have more effective and considerable impacts on sustainable rehabilitation [20]. Rating systems can be applicable to the interventions involved in the thorough renovation of historic buildings but may not address the specific issues related to a sustainable valorization of the historical and cultural aspects of this particular segment of the built environment [21].

GBC Italia developed a protocol dedicated to architectural heritage, GBC HB (historic buildings), which has been applied a few times [22,23]. LEED protocols (new construction, homes, core and shell, neighborhood development) are addressed to new constructions or major renovations; only the Italian GBC HB considers the refurbishment and the certification of the sustainability level of interventions. GBC Italia has developed a guide dedicated to neighborhoods, historic buildings, and the management of existing buildings. These studies have highlighted the compatibility between the safeguard requirement, maintenance, and preservation of historical contexts with current needs and future provision for energy efficiency [24]. An exemplary model is Savona, Italy [25]: the project reached the gold level of USGBC's LEED for Cities, increasing the efficiency of the energy management of the whole urban area by the adoption of LEED certification as a planning tool and the fulfilment of city development interventions, with the purpose of improving the lives of citizens.

USGBC guidance for applying LEED certification does not propose a method or a strategy for the calculation of LEED requirements, but refers to the professional experience of technicians and stakeholders for achieving the certification. The complexity of options and the required documentation complicate the process to achieving a LEED certification, often deterring technicians and surveyors from approaching the rating system process. The goal of this work was to create a methodology for selecting aspects to consider and the credits to calculate according to the project characteristics [16]. This paper presents a new procedure for optimizing the integrated environmental and energy audit dedicated to historical buildings, referring to the general scheme of the energy diagnosis process defined in the UNI CEI EN 16247-1:2012 standard [26] and to the LEED Operation and Management (LEED O+M) rating system that focuses on the management and operative aspects of a building. A specific procedure for the application to historic buildings was implemented starting from previous proposals [27,28]. A univocal and unambiguous workflow that optimizes the effort on assessment process and the resources, reaching higher levels of sustainability and energy efficiency, is presented.

LEED O+M is used to analyze the operative and management aspects usually aimed at existing buildings [18], even if it has been applied in a few cases to historic buildings [29]. LEED O+M can be usefully applied to historical buildings where the management is not interested in a complete renovation or in a complete conservation project. In Italy, the protocol was applied to one historical building, the Ca' Foscari University headquarters in Venice [30], and the Galleria Borghese in Rome is a case study for a future application [31].

Here, following some previews works [32–35], the authors propose integrating LEED O+M with green audits to guarantee a sounder evaluation of the operating strategies to apply during the preliminary analysis of a retrofitting project. A case study of a museum is considered, Ca' Rezzonico in Venice (Italy), that is not interested in renovation or a thorough conservation project (as required for the adoption of standard LEED protocols) but is interested in green management and maintenance. The green audit is used to identify a better framework of the critical issues and the potential for sustainability of the building. The environmental assessment protocol was applied, choosing the issues and credits that most optimize time and costs to result in a high level of sustainability, good performance assessment by the protocol, and to ensure the effectiveness of retrofitting.
