The ultimate eco building

Its door handles are made of salt. Its walls are made of sunflowers. Its furniture is made of Japanese knotweed. And it was stained with dyes made from filtered urine. Is this recycling marvel in southern France the future of architecture?

In a former railway repair shop in the southern French city of Arles, flasks of lurid green algae are bubbling away on a shelf, in a room that looks like a cross between a modern-day laboratory and a witch's potion-brewing den. Nearby, a 3D printer spews out curious objects made from algae-based bioplastic, while samples of algae-dyed textiles hang on a rack. Some of the walls appear to be made of rice cakes, others look like Weetabix, while some are daubed with a coat of porridgy gloop. All are natural byproducts of the local sunflower industry, the mashed-up pith and fibres redeployed as acoustic insulation. Elsewhere, there are antibacterial door handles made of salt, harvested from the region's salt marshes; thermal insulation made from bales of local rice straw; and bathroom tiles made of waste clay from a nearby quarry.

You’ve heard of farm-to-table food? Well, this is farm-to-building architecture: the latest low-carbon weapon in the battle against the climate crisis. "We call it bioregional design," says Jan Boelen, artistic director of Atelier Luma. Given that the built environment accounts for around 40% of global CO2 emissions, he argues it is time we embraced locally sourced, organic methods of construction. "We need to move from globalised, extractive supply chains towards regional ecosystems of materials that help regenerate the environment. Where others might see waste, we see opportunities."

The atelier is the latest addition to Luma Arles, a vast contemporary art campus created by the Swiss billionaire collector and patron Maja Hoffmann, heiress to the Roche pharmaceutical fortune. She opened the 10-hectare park in 2021, trumpeting its arrival with a twisting metal tower by Frank Gehry. Below that, a once arid concrete expanse has been transformed into a lush oasis, and a group of 19th-century train sheds elegantly converted into exhibition halls by Annabelle Selldorf. The atelier is the final piece of the jigsaw and the most quietly radical of the lot: a living showcase of what a brave new bio-architectural future might look like.

Hoffmann grew up in Arles, where her father, Luc, was a pioneering naturalist who fought to conserve the region's Camargue wetlands and co-founded the World Wildlife Fund. She sees Atelier Luma as a means of continuing his work, but with a productive bent. "I wanted to move forward with conservation," she says, "without being a green conservative agent. We need to act."

The process began with mapping the region's resources, industries and waste products, identifying streams of both materials and local knowhow. Armed with Hoffmann's ample funds and an open-ended brief, a team of 30 researchers – with backgrounds in product design, chemistry, sociology, biology, economics and engineering – have been probing everything from algae dyes to sunflower leather. Following extensive testing and certification, many of these experimental materials were used in the actual building. "It will never be finished," says Boelen. "We see it as an ongoing testing ground."

The conversion of the handsome stone industrial shed into the atelier's home, christened Le Magasin Électrique, is the joint work of London-based collective Assemble and Belgian practice BC Architects. They were originally approached to compete for the job but, unusually, decided they’d do it better together. It was a wise move. Each has a long-running interest in repurposing construction waste – Assemble using "rubble-dash" render on a music venue in London, and BC making compressed blocks from earth excavated from building sites in Brussels. Through collaboration, they have upped each other's games, creating a magical place that oozes invention.

"We saw the building itself as a quarry," says BC's Laurens Bekemans, explaining how broken roof tiles were reused in the floor, embedded in a slick surface of polished terrazzo to form a kind of history of the building inscribed across the ground. Internal walls are made from rammed earth using a recipe that incorporates demolition debris and limestone dust from local quarries, mixed with white clay to create a concrete-like finish – with all the strength of that material but little of the embodied carbon.

Every surface reveals how it was made. The walls stand as monolithic, rammed masses up to first floor level, their crumbly compressed layers looking like sedimentary rock; then they continue as earth bricks above, where laying smaller blocks by hand was easier. There is a model-like clarity to how the pieces go together – another function of how the project was designed.

"We tended to communicate using big models, to get around language barriers," says Assemble's Joe Halligan. "So the result sort of looks like a blown-up model." He's right: details such as the oversized wooden lintels and chunky bannisters, with their joints expressed like chubby dowels, give the place the playful air of a giant doll's house. Assemble's Maria Lisogorskaya explains how the long, double-height timber gallery was inspired by Lina Bo Bardi's Teatro Oficina in São Paulo, bringing a theatrical touch to a row of workshops whose wooden structure was stained with a natural deep indigo dye.

Indigo is one of the plants being grown in the tinctorial garden outside, along with cacti for cultivating cochineal bugs, which are used for red dye, all fed by recycled grey water, as well as "yellow water" from the urine-separating loos, safely filtered through cleansing algae basins.

For the opening, the atelier's experiments in material alchemy are displayed on tables in the workshop, and the breadth is mind-boggling. Rice fibres have been woven into rope to create geo-textiles that help mitigate coastal erosion. Invasive species, like Japanese knotweed, have been turned into honeycomb panels and veneered with other invasive timbers to make furniture.

Along with the germ-fighting door handles, salt has been grown into lampshades and cladding panels by immersing wiry armatures in the marshes for a few weeks at a time. Some of the 5,000 tonnes of waste clay that a sand quarry produces each month is being turned into ceramics. If scaled up, the implications for these material streams are huge: just 5% of all the rice straw produced in France, say the researchers, would be enough to insulate every building in the country.

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Although rooted in the Camargue, the atelier has international ambitions, applying its bioregional principles to other contexts. Boelen's philosophy is: "Materials are heavy, so they should stay local. People and ideas are light, so they should travel." Projects include working with women in Egypt to make glue-free shoes using woven date palm leaves and camel hair wool. In the emirate of Sharjah, the team are working on natural air conditioning, using water-soaked ceramic blocks which the designers say can lower indoor air temperatures by 8C through evaporation.

Many of these partnerships come with financial incentives. Although most funding comes from Hoffmann, the atelier also operates as a consultancy to generate income. Boelen says they are working with a champagne brand – exploring how grape waste could be used for packaging – as well as "a huge European automotive group", though he won't go into details about that one. Might the future of transport be compostable?

The real test will be if the atelier can influence mainstream manufacturing, beyond the realm of gallery experiments and bespoke luxury products. Perhaps some of Hoffmann's patronage could be directed towards a model social housing project? Or a college to train a new generation of bio-builders? It feels jarring to see the atelier's eco-materials used as decorative appliqué in Gehry's bloated tower. There is sunflower pith wallpaper in the restaurant, algae bioplastic tiles in the loos, and crusty salt cladding in the lift lobby – all seductive touches, but they do little to mitigate the untold tonnes of carbon emitted by the steel, concrete and glass leviathan that towers above.

The 10-storey, €175m beacon of crumpled metal panels – a tossed-off signature from the world's most famous dial-an-icon salesman – feels sharply at odds with Hoffmann's professed ethos. The dissonance makes more sense when you realise she commissioned Gehry more than 15 years ago. After lengthy negotiations with Unesco, which polices Arles’ world heritage site status, Luma was eventually granted its tower – by which time it looked like an anachronism. Would she do it again?

"I needed a sculpture to capture people's attention," she says. "The town was gently asleep. People only came here for the old Roman city." For all its attention-grabbing extravagance, with its jaunty windows bursting from a twisting tornado of steel, the tower is underwhelming inside, mostly housing offices and back-of-house spaces. Bewildered visitors roam its gaping spaces, climb its helical staircases and wander its swooping landings in search of the galleries – which are buried in the basement.

Still, the combined effect of Gehry on one side and Assemble and BC on the other makes Luma Arles a fascinating case study. There are few other places in the world where it is possible to witness so clearly the end of one outmoded architectural era and the optimistic dawn of another.