From detail to concept, the housing tower Bois-le-Prêtre in Paris
Architects : Frédéric Druot, Anne Lacaton, Jean-Philippe Vassal

Text and photos Stefania Kenley

The detail invested with cultural authority seems to participate in a reliable circuit of architectural values. Constructive innovation and technological performance still represent the warranty of solidity, utility and beauty, following the Vitruvian classical model. However, a paradox has recently emerged and questioned this certitude : the performing detail conceived and drawn on computer seems to be indifferent to the crude reality of a world threatened by poverty and lack of culture. Thus, the undisputable trust in the well-drawn detail, useful and truthful, can not avoid two questions emerging from the present context : “with what means?” and “how much does it cost?”.

Confronted with these questions, the cult of the performing detail takes different forms in the construction of Social Housing, a kind of investment which still occupies an important place in France. Providing a percentage of social housing in each new project, dwellings destined to people with lower income, is a constant preoccupation of the public authority, through its representative body – the OPAC (Office Public d’Aménagement et de Construction). Sometimes these operations have as results a variety of explorations of innovative architectural tendencies and details carried out in the new Parisian quarters – Paris Rive Gauche, or more recently Clichy-Batignolles, La Défense/ Courneuve/ Nanterre and Boulogne-Billancourt. A new project needs to be proposed in a zone subjected to “concerted planning” – ZAC, Zone d’Amenagement Concerté – the urban detail is open to public debate, informed by explicit drawings and models and intended to ensure a continuous dialogue with the local inhabitants. The success of this interactive process depends on the fine balance between public funds and private investments in the joint venture of a SEM – Société d’économie mixte . The negotiations for land purchase include the engagement of private investors to finance the projects of infrastructure and of Public space .

These large scale urban operations propose an excellent lot of new housing but which unfortunately covers only a small percentage of the current demands. In this wave of investment in new dwellings on cleared land, the possible re-use of the existing buildings has been rather underestimated. One should recall that the demolition of the housing blocks which were considered ghettoes of the post-war period had as a side-effect the increase of housing demand on an already too long waiting list.

Such a question was raised in relation to a housing estate in the North of Paris, in particular regarding the 50m tall building called Bois-le-Prêtre, designed by Raymond Lopez in 1962 . This 16 floor housing tower-block is situated at the limit of Central Paris near the Périphérique ring road, a zone poor in social and commercial facilities. Going beyond an initial plan of demolition, the OPAC de Paris organized a competition envisaging the fit-out intervention for bringing it to contemporary living standards. The competition was won by Frédéric Druot, Anne Lacaton and Jean-Philippe Vassal who had previously proposed a coherent strategy of refurbishment and extension of obsolete housing blocks . Taking into account the gloomy future of the low income tenants, the architects imagined an assemblage of prefabricated elements that would not displace them during the building works. In this complex process the architect Frédéric Druot was responsible for construction and site supervision. Anne Lacaton describes this process as following :
“The project has been made for, and with, the inhabitants of the building. Since the beginning of the competition project, we have established the principle that the tenants would not have to move away during the construction work and would stay on afterwards. They were organized in an association and so they took part in a process of concertation and actually remained in the building during the building work. This was a very important objective of the project which has therefore determined the construction system concept and detailing.”

The building site was organised on the perimeter of the housing tower but leaving free access to the common space leading to the upper flats. This access was enhanced by the construction of two more lifts with translucent inner and outer faces, allowing some light inside the staircase landing and a glimpse outside. (2) The flats are extended with a self-supported metal structure on foundations that are added to the existing structure. On the long sides of the building, the living area of each flat is extended beyond the limit of the existing façades on metal platforms of 3×7.5m, in order to become a winter garden and a large glazed balcony. (3) On the short sides, lager extensions are destined to increase the floor area of the apartments occupied by families that grew larger, a solution that has been developed in dialogue with the inhabitants.

Although the concrete structure is preserved, the façades of prefabricate panels, with reconfigured windows and added insulation in 1980s, is replaced with large double-glazed bay windows, forming the first layer of the extension. (4)  Through the design detail of terrace enclosures doubled by thermal curtains, the winter gardens are expected to increase the passive energy, reducing thus by 50% the consumption during the cold season. (5) To respond to the individual demands of each family, these new elements have played a role not only in the energy saving but also in reshaping the spatial configuration of the flats, getting rid of unnecessary walls. The initial surface of 8900m² corresponding to one hundred flats has thus been extended to 12460m². The nature of the building works is likely to keep the rents and the maintenance costs down, while the technical and spatial improvements are supported by the local authority, in an action that everybody – architects, client and tenants – wish exemplary.

This intervention demands careful detailing, often more difficult than the effort invested in new-built dwellings. This professional and civic eagerness to refurbish an existing block can bring us to important observations. In this particular case, the working detail leads to a clear design concept where the housing tower is no longer a symbol of social segregation. The refurbishment and extension of this existing building represents a polemic gesture in relation to the plans of building new tower blocks in Paris – an urban centre of ten million inhabitants from which only two million are living in Paris intra-muros. The solution of tall buildings (efficient from an economic view point) has been heavily criticised and, after several public meetings, abandoned. The only “towers” that have obtained for the moment the right to exceed the current limit of legal height in Paris are the office buildings. In this debate centred on the height of the future object, the architects Druot, Lacaton and Vassal plead for good living standards offered to all, through a careful reconfiguration of already existing flats.

Bois-le-Prêtre tower brings us back to the principle of a simple but apparently forgotten spatial organization, proposing a clear volume and generous usable area, with flexible openings towards light and air. The re-evaluation of a historical concept through the working detail gives a new reason for re-thinking our view on modernist mass housing projects. Maybe we should condemn less the post-war housing estates than the misuse of prefabricated concrete, badly assembled and finished. Maybe their failure was caused first of all by this poor detailing, not properly worked out and financed. Maybe after a long and costly detour through the urban sprawl of individual houses and a formal exuberance destined to a minority, we can re-visit the history of the Modern Movement and remember that “God is in the detail” .

In the specific case of Bois-le-Prêtre transformation, there is no worship of the construction detail for its own sake, or to the tower as architectural form. The detail is not an aim, but an effective and competent way to serve a social purpose. The central objective of Druot, Lacaton and Vassal is to improve the life conditions of the inhabitants that were threatened with displacement. On a Sunday afternoon, while visiting this building site approaching completion, I was impressed by the welcoming and polite attitude of the inhabitants – “Good afternoon ! Please come in ! Would you like to take the lift ? it’s new !” – all seemed proud of this achievement. In his work Histore(s) du cinema , Jean-Luc Godard noted with bitterness that no film was ever able to stop a war. This phrase can be more or less true for the cinema but, after this direct contact with the building site of Bois-le-Prêtre, I came back thinking that the architecture can influence people’s minds and behaviour.