**1. Introduction**

In this period, cities are facing many challenges related to different issues as climate change, demographic growth, social inequalities, economic crisis. The United Nations (UN) declared that 68% of the world population expected to live in urban areas by 2050 [1]. This means that the aforementioned challenges will be increasingly concentrated in urban areas. So, cities play a key role in the sustainability of our future. For this reason, international institutions (such as the UN) are actively moving in promoting actions to achieve sustainable development.

In this paper the attention is focused, in particular, on the role that cultural heritage can play in sustainable development. Although the debate around this issue is very current, many discussions remain on a mostly theoretical level.

In the 2030 UN Agenda for Sustainable Development [2], cultural heritage is explicitly mentioned only once in goal 11 (one out of 17 goals) that referred to the cities, in particular to the need of making cities and human settlements "inclusive, safe, resilient and sustainable". It has a marginal role in the document, being mentioning in particular only in target 11.4 ("strengthen efforts to protect and safeguard the world's cultural and natural heritage"), one out of 169 targets. Furthermore, this specific target is referred only to the *protection* and *safeguard* of cultural heritage, and not to its *valorization* and *regeneration* [3].

The "translation" of the principles of the 2030 Agenda in the cities, that is their territorialisation, is represented by the New Urban Agenda [4]. Here cultural heritage takes on a more important role. In fact, there are many points (i.e., points 10, 26, 38, 45, 60) of the document highlighting the role of cultural heritage (both tangible and intangible) in urban sustainable development. For example, the roles that it can play in the humanization of cities (point 26) and in developing vibrant, sustainable and inclusive urban economies (point 45) are underlined.

Furthermore, there are some international organizations, such as the UN Educational, Scientific and Cultural Organization (UNESCO) and the International Council on Monuments and Sites (ICOMOS), that stress the importance of cultural heritage in the achievement of sustainable development [5–7]. A very significant contribution by UNESCO to the international debate about this issue are the Historic Urban Landscape (HUL) Recommendations [5]. These recommendations recognize the necessity of supporting the protection, safeguard, conservation, and valorization of the Historic Urban Landscape, that is the «historic layering of cultural and natural values and attributes» ([5], art. 8), incorporating the intangible dimension of heritage and the related economic processes. In this document, the attention shifts from the "monument" to the context, to the recognition of the importance of the social, cultural and economic processes in the conservation of urban areas ([5], art. 4).

In the same perspective, the European Commission (EC) has recognized cultural heritage as a common good representing a strategic resource for sustainable development. In Section 2 the EC identifies it as a key element in the global competition using, for the first time in an institutional context, the notion of "intrinsic and social value of heritage" [8].

Many issues at the heart of the contemporary world debate concerning our future intersect with the theme of building reuse, ranging from the research of sustainable development models to the protection of cultural roots. Reuse is consistent with a sustainable approach to urban and landscape management, according to a model of "circular economy" capable of turning «goods that are at the end of their service life into resources for others, closing loops in industrial ecosystems and minimizing waste» [9] (p. 435). Nowadays, in line with instances of climate justice and the living planet, «it is unthinkable for anything to have no function, to be useless, to make no contribution to the betterment of society. The contemporary mantra "Reduce, Reuse, Recycle" is testament to this essential prerequisite of contemporary life. Everything has to be useful, and existing building cannot escape from this agency of usefulness» [10] (p. xviii).

There is an urgent need to make this principal operational and thus "to move from principles to actions" (Agenda for Sustainable Development art. 39–46, New Urban Agenda points 126–160). To this end, new approaches and tools are required.

The research question aims to understand the relationships between the implementation of adaptive reuse projects and their success (or not) in terms of impacts on the buildings themselves and on the urban context. After a review of the relevant literature related to the adaptive reuse (Section 2), the assessment framework (including multidimensional indicators) for evaluating the impacts of heritage conservation and rehabilitation projects is described through the analysis and comparison of two Italian case studies by a survey (Sections 3 and 4). The choice of the case studies has been oriented to two similar adaptive reuse projects by the same architect and in the same place in order to highlight exclusively the relationships between the intended use and the impacts on the context. The results of the investigation are then examined and discussed to answer the research question (Sections 5 and 6).

### **2. Review of Relevant Literature**

Adaptive reuse, defined by Douglas as «any building work and intervention aimed at changing its capacity, function or performance to adjust, reuse or upgrade a building to suit new conditions or requirements» [11], allows conserving the different values of cultural heritage, both the use value and the intrinsic one. It allows extending the life cycle of a building, in line with the circular economy principles [12] that aim to prolong the lifetime of resources as long as possible and avoid resources consumption.

Building reuse is considered a means for conveying the legacy of the past, which consists not only of heritage buildings as physical items, but mainly of the wealth of information provided by each item. The reuse experience dates back a long way, but today we have a deeper understanding of its strategic importance. Considering the built environment as a resource does not only mean acknowledging its value as a result of human work or as a useful object. The built heritage can also acquire value for its talent to tell stories, to transmit knowledge, to recall the past, to be a symbol of events, traditions, shared knowledge, religions; in other words, it can be a source of cultural value.

To redesign a heritage building for new uses, knowledge of its history and past uses is critically important. A careful identification of exterior and interior architectural elements is needed to define the building's identity and assess the impact of the changes that the new use requires.

Since the 19th century, scientific debate has focused on the significance of physical evidence from the past and on the conservation of architectural heritage with cultural value. At the end of the 18th century, the sale of ecclesiastical properties confiscated by the State during the French Revolution in many cases brought about a change in their use as a production or military site [13,14], with transformations driven by functional and financial ends [15]. In the 19th century, «the needs linked to the new and even more complex functions, created as a result of the Industrial Revolution, as well as a new economic soils regime, whereby land value—rather than buildings—is the key to making a profit, encourage demolishing and rebuilding rather than adapting and adding» [16] (p. 6). As a reaction to these trends, the first theories on the relationship between conservation and transformation of the vestiges of past epochs have been developed; from these theories different positions have emerged.

To develop the idea of reusing the built heritage as a preservation strategy, the 20th century must be awaited. The Athens Charter, released by the International Museums Office in 1931, recommends «maintaining whenever it is possible, the occupation of monuments which can ensure the vital continuity, provided that the modern destination will be such as to respect the historic and artistic character» (art. 2). Nevertheless, only since the 1970s building reuse can be considered as an autonomous discipline. Indeed, just after the Venice Charter, which in 1964 affirmed the role of reuse as a means of conservation, the international scientific community focused its interest on this topic with conferences, articles and books. In 1972 a special issue of the journal *Architectural Review* entitled "New uses for old buildings", edited by Sherban Cantacuzino, was published. In 1977 two symposia entitled "Old into New" in Glasgow and "Old and New Architecture: Design Relationship" in Washington were held [17–20].

Research by Bie Plevoets and Koenraad Van Cleempoel [14,20,21] has effectively described different theoretical approaches to the topic of adaptive reuse, coexisting throughout the scientific debate over the last 50 years: the typological approach, which examines compatible uses for specific building typologies [11,13,22]; the architectural approach, which analyses the morphological relationships between old and new and the different design strategies (for example, the addition of new volumes inside, above, around the existing building) [23–25]; the technical approach, which focuses on building adaptations required to meet the needs of safety, comfort and usability (fire resistance, thermal behaviour, acoustic performance, etc.) [26–29]; the programmatic approach, which starts from the choice of a specific function and compares it with buildings available for reuse, in order to select a building suitable to accommodate such function [15,30]; the approach of interior design, which focuses on the "soft" values of the building (immaterial aspects, atmosphere, narrative), with the focus on protecting the "meaning" of the building rather than preserving its physical integrity [31–33]. Each of these theoretical approaches can be related to many reuse projects, as a principle of inspiration or as a deduction from past experiences.

The work of Italian researchers, developed through studies dating back to the 1970s, 1980s and 1990s, is based on the performance-based building design approach as a key to forecasting the results of adaptive reuse at the project stage [34]. Such an approach aims at establishing a system of rules to evaluate the existing buildings, considered as «organisms able to evolve and live in symbiosis with the needs of the people» ([35] p. 2). The rehabilitation project should choose what to preserve and what to transform, through an iterative process of information/decision [36].

Since the 2000s, multi-criteria assessment methodologies have been applied in research aimed at choosing new uses for heritage buildings, to find a balance between conservation and adaptation needs, as well as to define the preferable new function in relation to the impacts on the urban context [37–41].

An important issue in adaptive reuse projects is related to the "admissible limits for changing", and thus related to the compatibility between intrinsic values (values linked to history and collective memory) and new use values (that is the problem related to the suitable "choices") [42]. The starting point for choosing the new functions (use value) in the adaptive reuse projects is thus represented by the intrinsic value. It can contribute to orient choices for the most appropriate use for cultural heritage regeneration, adapting its use to changes in the needs of society and, at the same time, conserving its intrinsic value, minimizing the negative impacts on the urban context [42].

The reuse project involves a preliminary evaluation of the building, to identify criteria for the preferable design choices. These derive from the system of values ascribed to the building and its potential use. A wide-ranging scientific literature on the subject of reuse highlights the potential benefits on an urban and territorial scale, such as the increase in the market value of soils and buildings, social promotion and economic development in the surroundings [26,43]. The adaptive reuse can contribute to sustainable development producing, at the same time, multidimensional benefits: «cultural benefits (conserving "alive" a symbol of community identity), economic benefits (in terms of increase of productivity), environmental benefits (i.e., reduction of resource consumption) and social benefits (i.e., employment)» [44].

New functions may encourage new public and private investments, promoting the development of related activities and the provision of support services in the area in which the reuse project is carried out [11,45].

### **3. Case Studies: The Ancient Market and the Basilica of Saint Peter the Apostle in Ortigia**

Siracusa is a coastal town in the south-east of Sicily (about 121,000 inhabitants in 2019), founded by the Corinthians between 734 and 733 BC and called "Siracusa" by the ancient Siculan language Sùraka (meaning abundance of water). Included in the UNESCO World Heritage List in 2005, the city preserves everywhere memories of its ancient history, classic and Baroque works in spectacular scenery (Figure 1). Thanks to an enviable geographic position, since the Greek period Siracusa has been the junction of commercial exchanges and melting pot of customs and traditions of the populations (and of the dominations), that have succeeded in the Mediterranean area: from the Byzantines to the Bourbons, from the Arabs to the Normans up to the Aragonese. During the Classical period it was one of the leading urban centres of the Mediterranean basin and, because of its geographical position, it played an outstanding role in trading and cultural exchanges until the Middle Ages. As a result of the heavy earthquake of 1693, the town was rebuilt in Baroque style. The homogeneity of the style and the widespread use of light-coloured limestone, as well as the particular location of the old town on Ortigia Island, strengthened the urban identity of Siracusa, coming from the fragile balance between tradition and innovation, technical knowledge and creativity, built environment and nature [46].

**Figure 1.** Three views of Ortigia: the eastern seafront, S. Martino and Minerva streets. Source: photos by the authors.

In the 1950s, the most important chemical and petrochemical industrial centre in Europe developed in the Siracusa area, where oil refining, derivative processing and energy production were carried out [47–49]. For decades this provided the main employment opportunity for citizens of Siracusa. Since the mid-eighties, industrial activities have been significantly reduced, leading to serious reconversion problems and the need for land decontamination. In more recent years the situation has changed. The decline of the chemical industry is driving investment in agriculture, food industry and tourism. In particular, this latter activity has developed as a result of the policies implemented by the local government over the last 30 years. Exceptional historical and artistic testimonies and the outstanding landscape value of the area, which combines cultural heritage harmoniously with natural resources, are driving an increasing number of people to visit the site and in 2005 this resulted in the inclusion of the town, along with the Rocky Necropolis of Pantalica, in the UNESCO World Heritage List.

Ortigia Island (Figure 2) is the main attraction for visitors, alongside the Neapolis area, which is almost completely devoid of tourist facilities. Ortigia is located at the eastern end of Siracusa in an area of 45 hectares. Two bridges across a narrow channel connect the island to mainland Sicily. Nowadays, the island is an extremely popular place for tourist accommodation, shopping, food and entertainment. This is the result of political choices and investments over the last fifty years.

**Figure 2.** Ortigia Island. Source: www.flickr.com, author: Falk Petro, 2016, no changes were made [Attribution 2.0 Generic (CC BY 2.0)].

Since the beginning of the 20th century, Ortigia has been affected by a progressive decrease in the number of inhabitants. The depopulation process was particularly marked after the Second World War and overlapped with the expansion of the town on the mainland. The Ortigia inhabitants dramatically decreased between 1960 and 1970 from 23,000 to 12,000 units, up to 5994 in 1991 [50]. In recent years, data show that the number of residents has stabilised between 4450 and 4550 from 2003 to date [51].

The subsidies granted by the Regional Law for Ortigia (1971) and the special law no. 70 on "Protection of the historical centres and special regulations for the Ortigia district and for the historical centre of Agrigento" (1976) are the leading factor behind the depopulation of the town centre in the 1970s and 1980s [52]. Such laws had the purpose of implementing strategies of conservative restoration for heritage buildings and urban rehabilitation in the old town. In addition, the special law no. 70/1976 authorised the variant of the General Regulatory Plan of Siracusa through the Detailed Plan for Ortigia, drawn up by Giuseppe Pagnano and approved in 1990. The urban renewal policies arising from the Pagnano's plan were implemented in an area characterised by deep physical and socio-economic degradation. Most of Ortigia's population was destitute and its displacement to other neighbourhoods was considered a necessary condition to accelerate the process of urban rehabilitation. The strategy of the Detailed Plan is based on the reuse of the building heritage to combine housing, tourist and accommodation services, cultural activities, headquarters of local government, university and education. Minor physical transformations were planned for the old town centre, but significant changes were expected in the use of the buildings. The investments concerned not only the conservation of cultural heritage, but also the creation of culture, as "one of the most powerful engines for the functional and economic revival of the historic center [...] able to build significant processes of reuse in disused areas of the island" [53] (p. 167). The implementation of the plan mainly encouraged the development of tourist and cultural activities in the historical centre, and increased hotels, restaurants and commercial activities for guests.

The process of urban rehabilitation has progressively extended beyond the area of the main tourist attractions (Duomo, Fonte Aretusa, Castello Maniace, Museo Bellomo, etc.) towards other urban areas (such as the ancient Jewish district of Giudecca) and the waterfront. Nevertheless, Ortigia still retains degraded areas, borderline to the tourist circuits. In particular, marginal areas such as the Graziella district and the Market district retain a large number of abandoned buildings and are perceived by the inhabitants as unsafe areas. Even the reuse of heritage buildings for public use is not always as effective as it should have been in terms of increasing local vitality, attracting new users, and encouraging private businesses.

In order to verify the research hypotheses, the Ancient Market and the Basilica of St. Peter the Apostle have been analyzed as examples of reuse of public buildings in marginal areas of Ortigia. These reuse works, both designed by the architect Emanuele Fidone, professor at the Master's Degree Course in Architecture of the University of Catania, are good examples of a compatible adaptation. Although such cases have several common characteristics (location, designer, public use, public client, acknowledgements and awards for the quality of design), the impacts on the urban context seem different.
