Déchelette Architecture’s rammed-earth residential

In 2021, Déchelette Architecture won a competition organised by Seine Ouest Habitat et Patrimoine for an apartment building at 17 Rue des Quatre-Cheminées in the western Paris suburb of Boulogne-Billancourt. The brief called for a four-storey building with eight social housing units and a shop, using a timber structure and environmentally friendly materials.

The design developed by the Paris-based practice – led by Emmanuelle Déchelette and her brother Philibert – reflects its belief that ‘the construction world must evolve by using low-carbon materials and embracing the intelligence of frugality without compromising the aesthetic and poetic quality of architecture’.

The material palette largely comprises raw, bio-based materials requiring little processing: a cross-laminated timber frame, a stone façade to the ground floor and – most notably – rammed earth used in prefabricated blocks for the principal facade above. This is the first time self-supporting raw earth has been used in a four-storey French residential building but, as Emmanuelle Déchelette told RIBA Journal, the ease and advantages demonstrated at Quatre-Cheminées could encourage much wider adoption.

Prefabrication is not the conventional approach to rammed earth. Why did you choose it?

This is our second rammed-earth building. At the first, a three-storey private house in Paris called Casa Franca completed in 2023, the earth facade was rammed in-situ by hand. That took two months per storey – one for framing and ramming, the second for drying, which took longer than usual as it was winter. The whole facade took about six months to erect. At Quatre-Cheminées, by contrast, the earth facade is one storey taller but was constructed in under a month, using blocks that had dried off-site for three months. Speed and a clean, dry process were both desirable in a city-centre site.

Prefabrication also cut the cost of a rammed earth facade almost by half. Our first rammed-earth project had some complicated details and we appointed an experienced traditional builder from Grenoble to do the work. For Quatre-Cheminées, the blocks were made by a specialist company, Terrio, but installation was by a general building contractor that had never used the material before. They understood that it would be very easy to do, using the same techniques as for laying stone. The only special instruction we had to give was to protect the blocks throughout the process.

Were there any major complications to resolve?

Not really. It’s interesting that people are very curious about earth construction and have so many questions but, when you actually use it, you understand how simple it is. We didn’t need to do any strength or compression testing as the earth we use is always taken from somewhere where it has already been tested.

The blocks are not stabilised by adding cement, which is often used with rammed earth construction. It’s not necessary and we don’t believe in doing that. Adding 5 or 10 per cent cement to an earth wall comes at a high cost in terms of embodied carbon. And as the facade is 500mm thick it would be like doing a really bad concrete wall. In our first rammed-earth building, we did use a little cement in a few details but never mixed into the earth. That’s a red line for us as it would prevent the earth from going back to nature at the end of the building’s life.

At Quatre-Cheminées we have a stone facade at ground level. Above, the rammed-earth blocks sit on steel angles at each floor level. Mortar joints between courses are lime and cement but, in retrospect, I think we could have done without the cement.

How did you develop the wall build-up?

Here in France, the development of regulations has not kept pace with growing interest in this material and we were required to thermally isolate the facade the same way as we would if it were concrete. That means metal studs, about 120mm of insulation and an internal plaster finish. It’s very silly because the materials are not at all similar and you lose many of earth’s beneficial properties. The main one is inertia as a way of combating the greater fluctuations in temperature that will come with climate change.

We are hopeful that regulation will change. The increasing use of bio-based materials offers not just the opportunity to reduce embodied carbon but to design in new ways – just as the novelty of concrete in the early 20th century inspired new forms of architectural expression and thinking about new ways to live.

Another current impediment is taste. We are currently designing another rammed housing scheme where the external walls will support the floors. It’s for a private developer and they were concerned that exposed earth would discourage buyers, so they insist on white interior walls.  

How did you approach the appearance of the rammed-earth facade?

Its colour is natural. We could probably have put a pigment in but it adds complication. We’ve tried to expose the earth wherever possible as it needs to breathe. And there’s no treatment against pollution; we will see how that ages the facade over the years. Perhaps it will darken the colour. We have had some graffiti and that was very easy to clean off: you just sand back the earth a little bit. There’s some loss of the stratification in the surface but, if you do it carefully, it’s fine. And of course, the whole facade will erode slightly over time. It won’t remain perfectly straight in the way that a concrete façade would.

Because of that anticipated erosion, we reduced the sharpness of some angles, for example in the chamfered window reveals. People ask about the facade’s lifespan and I don't have an exact answer. But if you look at many historic rammed earth buildings, you can see that they have long outlasted buildings made from concrete.

Are there lessons from this project that you will take forward into others?

We are currently designing our third rammed earth building, this time with timber floors supported by the earth walls. Each time, we’ve adapted our techniques or tried something a bit different. For the first, the ground floor was also made of rammed earth, which creates additional complications with conduit for electrical services. That’s one reason why we used stone at Quatre-Cheminées.

We also wanted to explore how we could start to sculpt the earth because it’s not at all like concrete so we can’t think of facades in the same way. That’s why we’ve added vertical accents – like chamfered window reveals – because they don’t affect rainwater run-off. They also allow south light into the flats despite the thickness of the wall.

One lesson we’ve taken into the next project is that to work well with earth, you have to use very simple geometries and avoid all unnecessary interactions between earth and other materials – installing window balustrades internally, for example, to avoid fixing into the earth.

More broadly, we have to question what the aesthetic of the post-carbon era might be. We shouldn’t see earth or other bio-based materials only as a technical solution but as something with the capacity for beauty that can inspire new ideas for the future.

In numbers

Earth facade height 12m 
Earth facade width 10m 
Volume of earth blocks 40m³