We have recently published an article on the problems detected in a large part of the housing stock in our towns and cities that were built during the second half of the 20th century, when the technical standards did not contemplate any vocation for energy saving or reuse: When construction was linear. Analysis of the energy sustainability of social housing in Spain (1939-1989). Los objetivos y conclusiones de dicha publicación os la incluimos a continuación.

Building circularly means thinking and design-ing for the future, so that, in addition to sus-tainability in construction, use and possible re-use, at the end of the building’s useful life, all the elements can be usable. Since Pearce and Turner (1995) set out their ideas on the circular economy, this approach has gained prominence in other disciplines, such as architecture (McDonough and Braungart, 2005). However, until very recently architecture has been ‘line-ar’, if we understand this as opposed to that end of reduce-reuse-recycle: the initial purpose was disconnected from the end.

Recent regulatory changes in housing construction pose a new scenario that brings our society closer to a protectionist awareness that, at least, reduces the speed of deterioration. This raises the relevant question of what to do with the tens of thousands of social housing units that have been built up to now, when there was no reuse approach, and volume, economy and speed of construction were paramount, especially in the context of increasing aid for refurbishment and adaptation to make housing more energy efficient.

The question thus arises as to whether it is possible that social railway housing, which is the subject of our study, can adapt more or less easily to the new regulations and thus contribute to energy savings for its tenants and society in general. As we know, social railway housing is generally characterised by the use of precarious insulating materials applied during its construction. For this purpose, we have compiled the information on the projects of the different developments studied.

Firstly, we must bear in mind that the technical standard governing the design and construction of housing in Spain was not approved until 1962 (M.V. standards), and consisted of a set of four groups of standards: actions to be considered for structural calculations, steel structures, brick masonry load-bearing walls and waterproofing of roofs with bituminous materials.Furthermore, it was not until 1979 that a compulsory standard was introduced for thermal insulation (NBE-CT-79), which remained in force until the beginning of the 21st century. Given this situation, it is logical to think that dwellings built in the period of our study (1939-1989) will encounter serious difficulties in adapting to the current situation.

Even so, we find in the Order of 29 February 1944 a series of precepts aimed at improving the hygienic conditions of dwellings, which was the main concern of the time, in order to avoid damp and lack of sanitation in the different parts of the dwellings. These recommendations focused on the adequate ventilation of the dwellings by regulating the minimum dimensions, the heights of the rooms, the surfaces of the ventilation openings and the minimum dimensions of the interior courtyards. With regard to the envelope, emphasis was only placed on insulation by means of a cavity or waterproof layer in ground floor dwellings, but there was hardly any reference to thermal insulation, with only a recommendation to protect the dwelling from the rigours of outside temperatures, without proposing either technical solutions or types of insulating materials.

For their part, in 1955, the technical ordinances and building regulations derived from the approval of the new law on low-income housing brought about some changes in terms of the concern for ventilation and insulation of the dwellings to be built, although these were still brief, with no specific insulation materials indicated for the proposed solutions. The interest in the correct ventilation of dwellings continued to prevail. The 1968 law is now more specific and, among other things, establishes a sanitary floor slab separated by a minimum of 30 cm from the ground for ground floor dwellings.

The result of the analysis carried out shows that none of the standard projects meet or even come close to meeting the requirements of the current regulations regarding thermal insulation and that comprehensive interventions on the building envelope would be necessary. Although it would be necessary to analyse each case, given that this is a representative sample of social housing in Spain built between 1939-1989, such interventions would require a significant economic effort that would be difficult to assume for the average income of the inhabitants of these dwellings and, in the case of ground floor dwellings, would be impossible to apply.Therefore, although only the energy saving aspect has been analysed with the aim of extending the useful life of the dwellings in order to meet the comfort needs of today’s society, the fact is that it would be difficult to apply in many of the cases studied.

However, a simulation of reality has been carried out with simplified calculations and model blocks in a favourable climatic situation. In a likely scenario of progressive global warming, this simulation still falls far short of what the real situation could be, especially in some climatic zones (De Luxán García de Diego, Gómez Muñoz and Román López, 2015).

For the real case, it is necessary to carry out concrete and individualised audits with detailed studies taking into account social as well as economic and energetic factors (Fernández Ans, 2019) and (Fernández, Rubio and Guevara, 2019).

In our case study, the values obtained show a high unfeasibility of comprehensive corrective actions. Furthermore, it should be borne in mind that 32% of the dwellings are located in very low-income neighbourhoods and another 49% are located in low-income areas, according to data published by the INE, which adds an economic barrier that makes any action more difficult. However, the low energy quality of the project types (in all cases, energy ratings E) indicates that any action in this direction will be an improvement.

The paradox is that, from an exclusively energy point of view, actions on the envelope become more necessary in cases of energy poverty where users cannot afford to spend on air-conditioning installations (De Luxán García de Diego, Gómez Muñoz and Román López, 2015). This situation is not unusual for almost three quarters of the dwellings studied. In this sense, passive strategies can be essential, although they require a high degree of subsidy.

An attempt has been made to apply the principles of circular architecture to these dwellings that are still in use, in this case to improve and adapt them to regulations on energy saving, with the intention of making their continued use more sustainable, considering the limitations and impediments that this entails. It is a difficult transition from linear to circular construction, especially in this type of housing where the income barrier is an additional limiting factor. Therefore, with regard to the question raised at the beginning about the possible application of the principles of circular architecture to pre-existing social housing, the truth is that it still seems more of a dream than a reality.

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