**2. Evidence of Underutilisation of the Built Stock in Historic Centres of Small-to-Medium-Sized Cities in Northern Italy**

The research analyzed the Italian Census data from 1991 to 2011, the last comprehensive available one, of 20 small-to-medium-sized cities in six regions of Northern Italy: Friuli Venezia Giulia, Veneto, Trentino Alto Adige, Emilia Romagna, Lombardia, Piemonte [15,16]. There is no official classification in Italy of what a small-to-medium-sized city is; the research adopted the range between 30,000 and 200,000 inhabitants, which is pertinent to the dimension of the urban centres in Italy [25–27].

The analyzed cities are Udine, Pordenone, Treviso, Vicenza, Conegliano, Bassano del Grappa, Ravenna, Ferrara, Parma, Modena, Brescia, Mantua, Cremona, Bergamo, Pavia, Trento, Rovereto, Novara, Alba, Alessandria. All their city centres conserve a built heritage of exceptional value, some of them—Vicenza, Mantua, Ferrara–are listed as historic centres in the UNESCO World Heritage

Sites, while some others—Modena, Pavia, Ravenna—have monuments included in the same list. The analyzed cities are a very relevant sample of the urban world of Northern Italy and host almost two million people of whom almost 10% lived in the historic centres in 2011, see Figure 1, Table 1).

**Figure 1.** The 20 cities in Northern Italy; the numbers are the percentage of housing units not occupied in the ZTL.

The municipal territory of every city was divided into three areas to obtain specific results and compare dynamics: The inner part of the historic centre identified as the controlled traffic zone (ZTL), the rest of the historic centre defined by the last defensive walls and the rest of the municipality.

The analysis shows unoccupied housing (labelled "abitazioni vuote" by the Census) in the entire historic centre increased on average from 16% to 26% and systematically exceeded the other urban areas where the share of the unoccupied stock increased from 9% to 14.2%. The situation is even more significant in the ZTL: In these areas, the percentage of unoccupied housing increased from 18.8% to 30%.

The vacancy rate in ZTL increases significantly in some cities, such as Udine, Treviso and Modena when compared to the rate of the other historic centres; in Treviso, for example, from 1991 to 2011, the percentage of unoccupied housing reached 41.8%, whereas it was 21.4% twenty years previously. The vacancy does not appear to be related to specific parts of the historic centre but appears to be a widespread process; in fact, in the majority of the centres it does not involve buildings in their entirety and this partial utilisation mitigates the perception of the phenomenon.

The vacancy rate, moreover, does not relate to the degradation of built stock nor is the decline of the population due to neglect: The large majority of buildings in northern Italian city centres, especially those whose heritage is particularly valuable, were largely restored and renovated in the 1980s and 1990s, as were the large majority of public open spaces; therefore, they are an available stock in acceptable conditions.

The value of these empty units has an absolute economic significance; in fact, the sum is 33,775 units out of a total of 130,084 in 2011, with an increase of 17,642 units since 1991. If this empty stock is assigned an under-estimated value of 1000 euros/sqm and an average surface of 100 m2—the average size resulting from the analysis the Census Data for the 20 city centres—it sums up to a value of 3.37 billion euros, 0.2% of the Italian GDP in 2011.


Notes: The cities selected for the analysis of the city plan are highlighted.

**1.**Synoptic table of some results from the Census data analysis.

**Table** 

*Sustainability* **2019** , *11*, 2614

In the 20 centres that were analyzed, the population is decreasing: −20.118 units since 1991, on average −10.35%, but exceeds −20% in Ferrara and Bergamo. This decrease is not directly proportional to the percentage of housing vacancy, and is clearly less relevant; this difference may be related to the deaths of single elderly people who often live in the historic centres and the arrival of foreigners. In fact, despite being almost irrelevant at the beginning of the 1990s, in twenty years, foreign residents have become a significant percentage of the inhabitants of the oldest parts of the city—in Brescia, foreign residents exceed a 24% share of the population, in Modena this share reaches 26%–with an increase of twenty times compared to the figures of the early 1990s.

The abandonment concerns not only residential units but also companies and institutions. The results regarding the companies operating in the historic centres are not homogeneous among the 20 cases and, very often, companies have not decreased in number, but have been re-organized with a significant reduction in employees, decreased by between one-fourth and one-fifth when compared to 1991, with an average decrease of over twenty percentage points (−20.1%).

The results regarding institutions in the historic centres are more clear-cut. The density of institutions in the historic centre—the units per hectare—continues to be higher than in the rest of the municipality, but has suffered a drastic shrinkage, decreasing between two-thirds and four-fifths compared to 1991. The variation in institutions is homogeneous and indifferent to the regional location and the total local units declined by more than 70% (−73.9%) in the twenty years considered. Similarly, the institutions' employees decreased in all cases, with an average reduction of one-third. The average decrease in the rest of the municipal territories is also important, but minor: −58.3% for the local units. This diminution is partly due to the rationalization of office premises following mergers and partly due to relocation in more accessible areas of the city.

The interpretation of demographic movements and property dynamics of the last thirty years in 20 small-to-medium-sized cities in the whole of Northern Italy reveals severe underutilization; original inhabitants have been abandoning the centres, partially substituted by immigrants, enterprises are significantly reduced, and many institutions have opted for new locations. The choice of new locations by households, public institutions and businesses is exceptional as well as paradoxical because the abandonment involves parts of the city that have most benefited from the community's resources for centuries, constantly improving infrastructures and public spaces both in the quality of service and beauty.
