In Biganos, in Gironde, raw earth houses, who would have believed it? – release

From April 3 to 6, 2025 in Bordeaux, The quartus endowment fund for architecture Organizes a series of urban meetings, workshops and explorations on how to design and live in cities. An event that Release is a partner.

For those who walk the green alleys of the new residential district of Biganos, at the edge of the Arcachon basin, the buildings recently out of the ground have, at first glance, nothing very singular or very indigenous. We notice their harmonious scale, their wooden facades, their generous balconies … But these new homes hide their local soul well. Behind the coatings and cladding, between the concrete screeds, a geosourced proximity material has however frayed an unprecedented place: raw earth, taken from a thin clay drawn from the Landes forest.

Emphasized in the early 2010s by the mayor Bruno Lafon, the ZAC (Concerted Development Zone) of Biganos – 850 new homes – was born from an urgent necessity: absorb the real estate and property pressure aroused by the imposing neighbor, Bordeaux. Since 2015, and the extension of line B, Biganos is in fact only about twenty minutes by TER or by car from the Bordeaux tram … The town (11,000 inhabitants) has therefore resolved to build, but not anyhow. At the developer (the Public Housing Office, Aquitanis) and the Urban Bostwork (the Landscapers Trouillot & Hermel and the 2PM urban planners) it proposed to innovate, to make the city differently. This bet was born, collective: impose raw earth brick on all operations in the future ZAC.

The bias, rare and daring on this scale in France, imposed itself. “Biganos has long been brick land. It sheltered up to 18 brickyards, before everyone disappears. Make this inheritance one of the landmarks of the project has rained ”explains Paul Rolland, whose agency, 2pm A, is « Coordinator urban architect » of the ZAC. There remained a detail investigating: the fine, elongated and rosy bricks, which the local briquetiers once produced were cooked. « Either one of the most energy -consuming materials that isunderlines Paul Rolland. To be ecologically relevant, they had to be considered raw and extruded. ”

Disdated by modernity, the “BTC” (brick in raw earth) is the subject, in France, of a recent rehabilitation effort carried by a handful of convinced, including the Quartus group which built with the architects Serge Joly and Paul-Emmanuel Loiret the project of the Gardens of Embruns. The object, when used indoors, has all the virtues. «  »In addition to a very low carbon footprint linked to the simplicity of its composition (water and clay, editor’s note) and its manufacture (drying in the open air), BTC regulates humidity and temperature ”recalls Paul-Emmanuel Loiret, one of the architects of the ZAC, a bite of raw earth. « It absorbs sounds well and, unlike almost all of the current materials, does not embark any chemicals. »

In the region, however, its production did not exist. To invent this, engineers and architects went to strike, in 2019, at the Dobourg Gate, a family brickyard rooted for decades in Barp, 30 km west of Biganos. The brickyards, stung, were dismantled without counting. « We are ceramists, then for us, it was pure innovation, without parachute »specifies the director, Marie-France Dubourg. « We put water, clay and hemp in a baker’s kneading and we looked for the right recipe. » With the architects, themselves supported by AMàCO and Craterre, two pioneering Grenoblois labs in the matter, the Duburg ended up succeeding. With their bricks, 2pm opened the way by transforming the ephemeral space of citizen consultation of the ZAC into a solid demonstrative house.

Each architecture agency then took hold of the material in its own way. Here for the interior partitions (NUNC), there in interior dubbing behind a wooden facade (Dumont Legrand), here again for the separative walls (Joly & Loiret)… « No one knew where we were setting foot, but everyone played the game, the first promoters »rejoices Paul Rolland (2pm A), surprised by an enthusiasm he did not expect: that of the Boïens. “The project awakened local and family stories. The ancients are happy that the local masons rework the brick. ”

Some, like the Duburg, would like to see this momentum extending. “The BTC lacks outlets. We would have to sell 10,000 m2 per year to ensure two full time. We are far away… ” « Like straw or hemp, raw earth continues to suffer from the syndrome of Three little pigs, says Paul-Emmanuel Loiret. We believe that it is fragile, that it will not last. The concrete lobby has done its job well! ” Biganos hopes to inspire. On the ZAC, around 400 of the 850 accommodation planned are finished and inhabited. And the formidable west wind may have breathed, none collapsed.