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When Swiss construction giant Holcim created a way to blend carbon-guzzling biochar with cement and mortar, it turned to Chilean architects Elemental to create a project for the Venice Biennale; concrete can be a hard sell in the West these days, but in developing countries it’s often the affordable, reliable material of choice, and therefore, it's important to improve its sustainable architecture potential. The result is the Basic Services Unit (USB) – a slice of a house – on show in Marinaressa Gardens and at Palazzo Mora in Venice, launching during the Venice Architecture Biennale 2025.
Explore Holcim and Alejandro Aravena’s collaboration: Basic Services Unit
Biochar is a charcoal-like material, formed from any organic waste, from food to sewage. Normally, this end-of-life matter releases CO2, but when it is burned through a process of pyrolysis, the emissions are halted (one kilogramme of biochar absorbs three kilos of CO2). The Basic Services Unit, made wholly from biochar mixed with regular cement and recycled aggregates, is a net-zero structure that is as strong, durable and fire-resistant as a regular concrete building.
As such, it offers a sustainable alternative to monotonous, unecological, low-cost housing. ‘In Latin America, houses are built by people, so they need to be part of the process,’ explains Elemental founder Alejandro Aravena, who won the Pritzker Prize in 2016 for his innovative social housing. ‘Holcim’s new decarbonising technology allows us to address the speed and scale of the housing crisis without putting any more strain on the environment.’
It's a continuation of Aravena’s 20-year development of incremental housing, whereby owners start with a safe, fire-resistant, architect-designed framework and build from there as and when they can afford to. More than 4,000 low-cost Elemental houses have been built this way in Chile. At the two-storey house in Venice, furniture, sanitaryware and a kitchen are painted in chalk next to the solid walls to show viewers how the dwelling would likely evolve. ‘Even if the authorities don’t want people to build, they will,’ says Araveno, ‘and what they create is usually more beautiful.’
Holcim CEO Miljan Gutovic adds: ‘We need to build faster and deliver innovative and sustainable solutions, and Latin America is a key area of interest.’ With a staff of 65,000 and operations in more than 50 markets, Holcim is trialling its biochar technology in 11 countries, among them Spain, where it has used biochar mortar; and London’s Wood Wharf, where cement has been mixed with biochar made from coffee grounds and wood. Elemental’s Basic Services Unit in Venice is the most high-profile application of the mat so far.
'The unit combines science, technology, sustainability, security and safety,’ says Aravena. 'When combined with common sense, local knowledge and community empowerment, people can take over and avoid repetitive, dull, anodyne solutions. It can solve historical issues of social housing.’