The reports issued by the UN in 2018 (1) indicated that, in 2020, many cities all over the world would face the challenges of managing a rapid urbanization in order of ensuring adequate housing and infrastructure, supporting population growth, addressing the environmental impact of widespread urban sprawl and reduce vulnerability to disasters.

In particular, although between 2000 and 2014 the percentage of the global urban population living in slums decreased from 28.4 to 22.8%, the actual number of people living in slums increased from 807 million to 883 million (1); moreover, damage to houses attributed to natural catastrophes shows a statistically significant increase from 1990 onwards.

The contemporary Colombian city development is linked both to historical-typological development and to political, administrative, demographic, economic, social and cultural issues (8). The exceptional nature of these conditions characterizes urban development in an almost univocal way, if compared to informal South American urbanizations.

The informal urban expansions are caused by several reasons, the main ones are the internal and external migrations, the demographic explosions, the internal conflicts and, in particular, the internal forced displacement (the so called desplazamiento forzado) (8). Defined in 2009 as “migration directly or indirectly caused by armed groups” (9) and, in recent times, as that “mechanism of self-protection of the population that has suffered massacres and the escalation of acts of violence and repeated fighting” (10), the phenomenon is recognized as that condition in which “people are forced to flee or leave their homes particularly in situations of armed conflict” and that “are generally subject to heightened vulnerability” (11). In Colombia the phenomenon assumes an unsustainable dimension, in the first half of the twentieth century. In fact, at the beginning of the last century, with the aim of financing the infrastructural network to support territorial development, the Colombian government issued a large amount of government bonds, purchased from the local landowning oligarchies. These oligarchies, upon bonds could expiry, requested their conversion into land to be cultivated, the same that many farmers, called campesinos, had made fruitful, even if they occupied it illegally: it had inevitably turned into a social and territorial conflict (12).

However, the phenomenon of desplazamiento forzado does not only concern the question of the campesinos or the historical issue of the conversion of large estates but is also connected with the years of violence (1948-1964) which led to a second wave of migration and the birth of the Revolutionary Armed Forces in Colombia - People’s Army (FARC) and other armed groups. It is in this period that over 2 million of displaced people (which at the time represented 10% of the total population) move to the big cities: in 1964, 71% of the men of Bogotá were immigrants from other areas of Colombia (13).

The internal forced displacement and the conditions of poverty and economic hardship of the population have pushed towards the phenomena of “neo-urbanism” (14) which see the massive migration from the countryside to the cities.

Latin America is one of the regions of the world in which a large number of people live in informal settlements (15). The informal urbanizations that result from the complex social phenomena of conflicts, migrations and internal forced displacement, take different shapes in cities like Bogotá compared to other cities (16). In Bogotá, for example, the predominant type of informal urbanization comes from pirate district (barrio pirata) or settlements carried out with informal negotiations without legal legitimacy; it is different in large cities such as Medellín, where informal urbanizations take on the invasion district (barrio de invasion) character: it is a temporary occupation of large areas of public property close to the city center or to large infrastructures without intermediaries (4). In most cases, the invasion district tend to consolidate on public land (residual areas or zones of lack of urban planning) while, the pirate district occupy mainly private land, fragmented residues of old estates, once large, without any control by the owners (4).

In smaller cities such as those of the Department of Boyacá, these phenomena can be observed in its primary phase and, consequently, it is possible to intervene more effectively (3).

During the 1990s, the legislator tried to intervene by making informal subdivisions compliant with urban planning standards (Minimum Urbanization Standards). The further popular housing policies conducted by the Colombian government, especially since 2014 when the reduction of housing problems in the country is a priority, lead to the definition of new tools: the Housing with Social Interest (Vivienda de Interés Social or VIS) and the Housing with Priority Interest (Vivienda de Interés Prioritario or VIP). These tools represent the strategy of the Colombian government for a global response to the multidimensionality of extreme poverty (3, 4). The extreme poverty is measured in 2008 by the Unmet Basic Needs and corresponds to at least two of the following factors: lack of education for children under 12; low level of economic independence; accommodation made with inadequate materials; lack of access to water and sewers. The VIS and VIP tools are intended precisely for people in such conditions, for those who have lost their homes due to natural or political causes, environmental disasters and to the victims of the internal forced displacement (recognized by the Colombian legal system with Law n. 387 of 1997).

The difference between the two instruments is that the VIPs do not foresee any contribution from the final recipient while the VISs are partially subsidized (Law n. 1537, 20 Jun 2012. by which rules are issued to facilitate and promote urban development and access to housing and other provisions are issued) (3).

The market trend from 2011 to 2017 describes how the mentioned tools had an initial effectiveness but a subsequent decrease in this effectiveness (noticeable in the case of VIP and less in the VIS) when these tools became part of the stable policies in the country. In the fourth quarter of 2018, 27.2 million m2 of housing were built in Colombia. Of these, 23.3% (6.3 million m2) are for VIPs and VISs. The number of people currently living in conditions of housing deprivation is difficult to quantify, due to both the absence to a census of people living on the verge of legality and to the instability typical of housing temporality conditions, in particular for the victims of internal forced displacement. The latter were granted legal status with the aim of protecting them and monitoring the socio-demographic and urban changes caused by internal forced displacement (4). However, the numbers provide a measure only indicative of the huge amount of people who may be attracted to the housing mechanisms of informal urbanizations. In fact, only the displaced population from 2010 to 2017 present in each district amount to between 1.000 and 60.000 (figure 2); this number is not exhaustive but contributes to the construction of an overall general and dimensional picture of the housing issue in Colombia.

In recent years, the scientific community has undertaken a series of interdisciplinary studies on spontaneous urban settlements, aimed both at understanding the phenomenon of informality, and at defining intervention and practices for the requalification (social, environmental, cultural, building, urban, etc.) and the inhabitants’ quality of life improvement.

In early 1980s, these studies began comparing two schools of thought (17): the first one argues that it is not possible to elaborate a general theory that can explain the processes of informal urbanization in the sub-continent and, consequently, qualifies them as merely local phenomena; the second one, aimed at the formation and support of supranational acts, tends to simplify and homogenize logics of informal Latin American settlements and to allow the development of general theories.

What determines the substantial difference between the two schools is how they address the phenomenon of informal urbanization, the first by framing the theme with an international theoretical approach, the second by considering the practical dynamics of the territories and then the possible definition of a theory that supported them. Currently (18), the international scientific community is aimed at considering both the local point of view, with the peculiarities of each type of informal settlement, and the causes of international scope that feed the problem.

The method applied in this research is in line with this latter orientation. The research identifies the Colombian context as a socio-political area of investigation and the informal settlements that insist on the territory of Sogamoso as a special case. These settlements are identifiable as informal by the United Nations criteria (19). The formation and consolidation processes of housing within the informal settlements of Sogamoso are characterized by progressive traits (20) and the use of unskilled labor in a family self-construction. This means that the houses have poor construction and spatial quality, are unhealthy, made with unsuitable materials and without systems that can guarantee situations of living comfort (figure 3).

In general, the house originates from a single non-specialized space, a rectangular basic cell, where mainly night and shelter functions are performed. As in the typical processes of incremental construction, house progressively evolves its minimum characteristics, which until then had ensured the essential needs of housing, then improved with the financial capacity of families. The construction techniques used and the materials are those of the local tradition of the occupants, therefore they can come from places even very far from the large city on whose margins they stand.

The general objective of the research was to solve housing problems by defining, with a deductive approach, the critical conditions of general housing and the international reference standards. With an inductive approach also, the research focused on the requirements and strategies replicable and implementable for the housing improvement and for the mitigation of buildings vulnerability.

The specific targets, which derive from the evaluation of the place’s physical scenario, identifying the direction of the research itself, can be traced back to three areas of trans-scalar and interdisciplinary nature:

At the urban scale it has been observed that the regularity of the settlement is determined by illegal subdivisions of large free areas adjacent to the consolidated urban settlement (figure 4): they are rarely residues of old abandoned latifundia and more generally areas that cannot be cultivated and cannot be converted into income. These areas are characterized by high slopes and therefore not very attractive for a building market that prefers regular expansion in flat areas: however, they are ideal for the consolidation of a clandestine market of low-cost areas. The size of the lots descends not only from the position and the morphology of the land, but also from the progressive occupation of the same. Therefore, those linked to the first settlements are the largest up to, for example, in Bogotá, in lots of 10x5 m, which are however completely saturated (20). In the flat areas or with a regular course, the lots have larger dimensions, while in areas with steep slopes, the dimensions decrease.

At the building scale, the informal neighborhoods of the main Colombian cities (20) show that, in general, the first specialization, starting from an undifferentiated cell and with daily activities that take place exclusively outside, is the separation of the sleeping area from a living one. Subsequently, the services are defined, first the kitchen and only as the last the toilet. This feature demonstrates that hygiene requirements are not a priority.

This is mainly justified by the difficulty in construction investing of immovable and expensive plants with uncertain ownership. As a first modification, 57.7% of the inhabitants specialize the primitive cell with the separation between the living area and the sleeping one, only 11% separate the toilet from the compartment intended for daily activities and even less separate the kitchen area. The second most compelling change is that relating to the toilet, which takes a quarter of the houses that have already carried out a specialization. In any case, between the toilet and kitchen, almost 40% of homes see this further specialization completed (20).

The improvement of the construction materials and the wall structural consolidation remain the last intervention priorities. The houses have no spatial quality, there are no thermal neither acoustic insulation, moreover, the lighting and natural ventilation are scarce or absent. For climatic reasons, thermal insulation is not a priority and is not governed by any legislation. As it happens also for many of the formal settlements, the socialization space is on the street. Even when planning VIS settlements, the function of “relationship space” is entrusted to an open space. However, due to the growing contraction, there is no patio, courtyard or garden and it is the street that takes on a social role, even when it does not exist or is not structured.

At the social scale the marginal areas have highlighted the existence of an economic micro-fabric, not only illegal or submerged but based on the weak attempt to enhance local activities, such as food or artisan type, which should be protected because often generated by the lack of access the formal economy and by unsustainable tax pressures. From the social inclusiveness point of view, there are areas with strong communities and representatives, attentive and inserted in more or less structured paths of social participation in the urban transformation. On the contrary, there are so isolated cases where the community is lacking or does not exist as in the case of some areas in Sogamoso. In the latter cases, the subjects to which the research has turned its attention, are strongly marginalized and excluded and with difficulty manage to be included in structured processes. The issues to be addressed concern both the individual problems and the collective ones (21).

The informality of housing is closely related to the informality of work occupations because of both the impossibility of accessing the housing right and the impossibility of accessing the formal labor market (due to lack of experience or discrimination) or find greater benefits in the irregular one (14). The housing size and character of the settlements in the Sogamoso area reveals that the informal neighborhoods are located adjacent to the historical fabric, represented by the typical regular grid (cuadrícula), or rather, the urban grid of the Spanish-based cities.

Due to the impervious orography of the city that rises on the peaks of the Andes mountain, some routes tend to orient themselves along the contour lines, thus agreeing not to planning but to the greater force of the nature, while the orthogonal paths to them face dizzying slopes, in some cases maintaining the primordial geometric structure but losing their functionality. This condition led to an expansion of the city in limited directions.

The morphological characteristics of the lots, generally impose distribution conditions within elongated rectangular lots in which, often, only the narrow road front remains free, highlighting numerous critical issues relating to lighting conditions and internal ventilation.

In light of the critical issues represented at the various scales, and in order to define and apply retrofitting actions on a sample of buildings in Sogamoso, the research group aims to not delineate a retrofitting “project” but of a retrofitting “process”, considering the involvement and participation of local actors. They were essential for acting with effectiveness: the inhabitants have participated with contributions of labor and materials, logistical support, validation of the diagnosis and of the proposals; Fonvisog, the municipal entity in charge of managing housing improvement emergencies, has provided information from the databases, control of regulatory aspects, availability of human resources, technicians and construction materials.

The construction characters of the houses contemplate the adoption of raw earth bricks or hollow bricks used in confined masonry with vertical stiffeners (more rarely horizontal) in weakly reinforced concrete, as required by Colombian anti-seismic regulations but hardly well made. Brick blocks are often reused, of low quality and of different productions; sheet metal or corrugated asbestos cement sheets are generally used for roofing.

The strategic actions are:

In addition to the Italian and Colombian university institutions, the design process of the strategic research phases (figure 5) involved the cultural association Architecture Emergency Development (AES), which operates in the field of economic, social and cultural promotion and for the international cooperation, and the National Social Housing and Urban Reform Institute. (FONVISOG), a decentralized public authority of Sogamoso that encourages and contributes to the construction of housing for eligible citizens, through the management of national, departmental, municipal and private resources.

With the aim of “reducing the housing deficit of the community for improving the quality of life (23)” the two subjects have played an important role for financing.

The methodology used in the participation process was based on retaking and implementing constructive progressivity, this being the typical mode of operation through which families self-manage the construction of their homes; the researchers provide technical advice to said progressivity, strengthening decision-making during the conception, management, construction and evaluation of the interventions.

The sample of buildings was selected identifying specific criticalities for housing quality related to technological and environmental aspects after the definition of the cultural and social strategies and the identification of the actors for the operational phase of the research.

For the evaluation of the interventions, the buildings were classified by using a dichotomous function based on the severity of the problems relating to the following characteristics:

Furthermore, the structural criticalities were assessed, and each building analyzed has showed poor seismic resistance (4).

The analysis results are synthetized in a map of interventions for the housing performance improvement.

This map is integrated through the participation of the inhabitants to whom a questionnaire was administered to establish their real housing needs. This questionnaire was used as a project tool for detecting and proposing interventions and led the design process through the consultation, negotiation and deliberation phases between universities, associations involved and individual citizens. The research established a truly participatory process aimed at inclusiveness of citizenship within the main nodes of decision-making: from the preliminary formative-ideational one, to the evaluative one (in terms of value judgment and choice judgment) up to the actual choice act (24). This made it possible to strengthen and integrate the existing rules with a positive character, so as to confer quality, recognition and consensus on the complex system of interventions.

With reference to performance improvement actions, classes of requirements have been identified as codified by UNI standards. In particular, compliance with the requirements of safety, well-being, hygiene and health, appearance and usability (as classified by the UNI 8289: 1981 standard) was considered a priority, leaving out the management, integration and safeguarding of the environment and resources rational use. The latter, acquired in the regulatory integration of 2008, fulfill the typical needs of a building fabric made in formal conditions of construction and is typical of consolidated construction that has already fulfilled the other classes of requirements, therefore, a very different context from that of informal settlements.

To the evidence of analyzed case studies, the necessary safety requirements referred to the mechanical resistance of the structures, those on the well-being and health to aspects relating to environmental comfort, to those on the appearance and usability of the internal environments in the construction elements as well as the accessibility of the structures.

Of the 40 houses intervened, with the objective of selecting the five buildings to be reinforced with reinforced plaster, the research group visited about 20 houses, of which 15 were discarded due to difficulties for their formal integration to the improvement (figure 6).

At the end of the case study analysis process, improvement actions were classified in relation to the following.

Figure 7 shows one of the cases studies.

The process ended with the monitoring of the interventions. In this sense, the tools of the participatory process were also aimed at the ex-post evaluation of the interventions.

In the ex-ante phase, the participatory process was applied on site and on the basis of numerous meetings with the local community, while for the ex-post phase a questionnaire was prepared which was subsequently administered to housing users. The questionnaire was carried out to have feedback from users on the habitability conditions achieved, and with the specific objective to obtain a punctual qualitative feedback focused on aspects relating to safety only (specifically to seismic vulnerability, because of the greater evidence and sensitivity on the subject also by the inhabitants and for the possibility of applying, adapting it, the evaluation method of the Colombian Association of Seismic Engineering).