A virtuous construction for Boulogne-Billancourt

At 17 rue des Quatre-Cheminées in Boulogne-Billancourt, the largest suburb of the French capital Paris, Déchelette Architecture has completed a four-storey building and a retail outlet using a timber structure and bio-sourced materials. The result is a remarkable exercise in frugality.

In January 2021, Seine Ouest Habitat et Patrimoine (SOHP) launched a competition for the construction of a timber-frame building in Boulogne-Billancourt. Déchelette Architecture won the competition. The Paris-based architecture firm's proposal involved the use of self-supporting raw earth on four levels of facade. The idea won over the client, and was a first for multi-family housing in France. It should be pointed out that the architectural firm, founded by a sister and brother who are aware of the ecological issues of our time, has from the outset favoured the use of materials with a low environmental impact. The Boulogne-Billancourt project is testimony to this.

Optimising various services

The complex is located on a city street with a so-called ‘faubourienne’ or working-class architecture that blends several styles and periods. Five storeys high, including a green roof, the complex is set on a deep plot of land, with the rear reserved for a landscaped garden. The front facade is aligned with the road. Built around a central core, the building comprises two through flats on each floor, with the living rooms facing the street and the bedrooms with large balconies facing the garden. The interiors are generously lit and the building's various energy requirements are optimised thanks to the transversal nature of the flats.

Raw and bio-sourced materials

In its quest for energy-saving and sustainable buildings, Déchelette Architecture has always turned to raw and bio-sourced materials. Apart from the ground floor slab and the core containing the vertical circulation, the building is made from three bio-sourced materials. These unprocessed materials reflect the architects' desire to introduce a number of construction cultures that combine common sense and sobriety. The choice of stone, raw earth and wood was therefore decisive. However, this has never been an easy exercise to apply, and even less so for a block of flats in France. But the architects didn't give up. They skilfully designed a self-supporting facade in prefabricated adobe with an ashlar base. The facade was assembled like a Lego in a very short space of time. It took just a few days to stack the different blocks, which had previously been dried in a workshop in the more southern Lyon region, where the earth also comes from. In this way, this age-old material with its many qualities is making a comeback in construction. This feat was achieved in collaboration with Terrio, a young company specialising in the manufacture of prefabricated raw earth blocks, which was also called in to carry out the structural work. It should be remembered that the window frames and various structural elements were made of wood. Thanks to the use of these materials, the whole project achieved HQE level 3 certification.

Off-site construction

With the exception of the ground floor slab, which was poured on site, the rest of the worksite was designed off-site. This was an essential part of our commitment to frugality. Thanks to off-site prefabrication, site time was considerably reduced, in turn reducing any risk of incidents. Cost reduction is also a factor. Thanks to this method, it cost less to erect, not to mention the ease of assembly, which avoided numerous inconveniences, such as noise pollution and waste. The architects explain that all the adobe blocks were shaped in individual moulds, using a gantry-mounted pneumatic pisoir, a hard wooden sledgehammer used to beat earth, and dried in their workshop before being transported to the site, then assembled in a month by three masons. This equates to between 12 and 15 m² of facade walls being installed every day. You can rightly say that Déchelette Architecture won its gamble with flying colours! In Boulogne-Billancourt it produced compact, simple and virtuous architecture that sets an example of frugality!