Social science research relies for the most part on consultation of archives and primary sources. This may seem obvious, but it is necessary to remember it because too often sources or re-elaborations of dubious provenance and unreliability are used in much research. As Carlo M. Cipolla reminded us, the social researcher differs from the novelist in that he does not invent what he tells, but reconstructs and organises his argument on the basis of the data he provides as a basis, through the notes that support this information. The results depend on his rigour in his treatment of the sources.

In our research, the consultation of primary sources, files and construction projects is an essential part of our project. So far, we have visited the 3 national archives and 29 municipal archives where documentation on the planning and construction of railway housing in the period we have set for our study is kept: from 1939, when the law on subsidised housing was published, to 1989, when the transfer of housing competences to the Autonomous Communities began.

Among the state archives, firstly, there is the Archive of the General Directorate of Architecture and Housing, which was managed by the National Housing Institute (INV) through the different ministries in which it was integrated, and which today appears within the varied collections of the historic Archivo de Fomento. The documentation located here is very valuable, extensive and diverse, and is especially related to the housing developments carried out by the railway companies, in particular RENFE.

In the General Administration Archive (AGA) we also found some projects in the railways section, although the most interesting collection is that of the accounting documentation of the railway workers’ cooperatives, which began to set up as developers of their own housing at the beginning of the 1960s. This documentation is particularly interesting because it is unique and different, but also quite uneven, since the information that these cooperatives were obliged to send to the INV varied in detail, although in general it is a very useful source for documenting the trajectory of these promotions.

On the other hand, the Historical Railway Archive of the Railway Museum of Madrid-Spanish Railway Foundation (AHF) is a very valuable collection of reports and references of the plans of the public company RENFE regarding housing and the relations with its employees on this issue.

The second block is made up of the municipal archives, as custodians of the documentation of files and projects carried out in the respective municipalities, which allows us to complete the information on the dwellings in almost all cases. In these archives, the consultation work is complicated, as it requires a visit in person. In this sense, the support and help of these local archivists has been very useful in locating the documentation fairly quickly, as their resources are scarce and not all the documentation is catalogued, which is part of the secular lack of our documentary heritage, both at local and state level. In general, accessibility to these archives is straightforward and simple, but we have found substantial differences in the consultation of the documentation, which has caused us some confusion, specifically in two areas.

Regarding the self-reproduction of documentation, the vast majority allow the researcher to collect data in this way, but 15% do not allow it, citing copyright, or even impose greater obstacles, such as permissions from the authors of the projects. A second section that hinders consultation is the introduction of electronic prior appointments that oblige the researcher to go from one window to another and, although some local councils resolve them well, in others this is not the case and requests take a long time without knowing for sure whether the consultation will be dealt with or not, which makes it difficult. This is not usual, but given our intention to cover all the documentation on railway housing in Spain, these limitations hinder our research.

As a final assessment, archives should be adapted to make them easier for researchers to consult, but researchers must also return to the archives. Our experience over the past months, through the many archives we have visited, is that their presence is becoming less and less common, which logically leads to an impoverishment of social science research. As we said at the beginning, the archive is the most solid basis for the proper rigour of any research.