To build or not to build; that is the question confronting a world on the precipice of change. With climate realities intensifying and global housing shortages escalating, the construction industry faces an inescapable dilemma on how to address the urgent need for shelter while minimising harm to the environment. It is a balancing act fraught with complexities, as each decision to build risks compounding ecological strain. Yet, the alternative, a failure to provide adequate housing, threatens human dignity and societal stability.

In this precarious landscape, the collaboration between Holcim, a global leader in sustainable building solutions and ELEMENTAL, the Pritzker-winning architectural firm led by Chilean architect Alejandro Aravena, offers a compelling pathway forward. By redefining what it means to build, their collaborative project, unveiled at the Venice Architecture Biennale 2025, seeks to transform buildings into proactive allies in combating climate change.

At the heart of this initiative is biochar, a charcoal-like material produced through the thermal conversion of organic waste. By integrating it with cement, mortar and concrete, the technology permanently traps carbon that otherwise ends up contributing to greenhouse gas emissions. This approach enhances the environmental performance of construction materials, ensuring they actively contribute to carbon sequestration while retaining their functional effectiveness. As per the design team, each kilogram of biochar used prevents up to three kilograms of CO2 from entering the atmosphere.

Discussing the nuances of sourcing raw material for biochar production, Edelio Bermejo, head of R&D at Holcim, tells STIR, “From Latin America, Africa and Asia, we source materials like corn, palm, coconut, agave, sugarcane and timber waste. In Europe and North America, sources include corn, tree pruning, organic municipal waste and timber waste. These diverse sources demonstrate the global adaptability of our approach to creating sustainable construction materials.”

The biochar technology is showcased in a full-scale prototype of a Basic Services Unit (USB), a housing concept rooted in the principles of incremental design by ELEMENTAL. The USB represents a continuation of Holcim’s efforts to address housing challenges sustainably. In 2023, the company partnered with the Norman Foster Foundation to create the Essential Homes Research Project, focusing on modular construction for displaced communities. The project emphasised scalability, rapid assembly and low-carbon construction, themes that are carried forward and expanded upon in the collaboration with ELEMENTAL.

"Our partnerships with architects enable us to push the boundaries of innovation to provide sustainable building solutions to our customers throughout the world,” Holcim CEO Miljan Gutovic shares with STIR. “In 2021, during the Venice Architecture Biennale, we developed a custom 3D printing concrete ink for Zaha Hadid Architects and ETH Zurich and, this year, we are partnering with ELEMENTAL to present new biochar technology that transforms buildings into carbon sinks.” 

Santiago-based ELEMENTAL has spent decades refining the "toolbox" to address housing demand, particularly in contexts of resource scarcity. A significant outcome of this area of work has been the incremental housing model, which provides essential energy and sanitation infrastructure while empowering residents to complete and expand their homes over time. In Latin America alone, the firm has implemented more than 4,000 iterations of this model over the past 20 years, demonstrating its practical viability and adaptability.

The USB presented in Venice represents a more radical distillation of this concept, focusing on core elements of living like shelter, sanitation and energy in a compact 21-square-metre unit. Equipped with a kitchen and a bathroom, the unit is designed for rapid assembly using precast panels and modular systems—an approach that not only ensures efficiency but also addresses issues of durability and safety, mitigating risks associated with uncontrolled self-construction. The unit’s design emphasises both immediate usability and long-term adaptability, allowing it to grow into a full home in response to the evolving needs of its occupants.

Highlighting the significance of this approach, Aravena, founder of ELEMENTAL, says, “In Venice, we are bringing incremental housing to its core: a structural sanitation unit using precast panels takes care of the basic needs of inhabitation. Holcim’s new decarbonisation technology allows us to address the scale and speed of the housing crisis's demand without putting a strain on the environment.” The vision aligns with the firm’s philosophy of addressing social challenges through innovative architectural solutions. Their previous projects, such as the Quinta Monroy housing development in Iquique and the Viña del Mar initiative in Chile, exemplify how participatory design can foster resilience and community empowerment. For instance, the Viña del Mar prefab provided residents with a structurally sound "half-house" foundation that could be expanded incrementally, addressing both affordability and density challenges in urban settings.

The USB’s precast construction method also offers distinct advantages in productivity, reducing labour requirements and timelines while ensuring high-quality, standardised outputs. The efficient assembly process is a strategic response to the urgent need for scalable, social housing solutions in rapidly urbanising regions. This is further complemented by Holcim's biochar-infused concrete, which combines environmental benefits with enhanced performance.

“Holcim is the leading partner for sustainable construction and we work with stakeholders across the value chain to deliver innovative and sustainable solutions for our customers," Gutovic continues. "Through our partnership with Alejandro Aravena and the ELEMENTAL team, we have demonstrated how Holcim’s new carbon sink technology can shape the future of construction.” The biochar-based concrete used in the USB prototype incorporates 100 per cent recycled aggregates, aligning with Holcim’s commitment to circularity and waste reduction. This initiative is part of a broader portfolio of sustainable solutions offered by the company, including ECOPact concrete, ECOPlanet cement and ECOCycle® circular technology, which aims to minimise the environmental footprint of construction across diverse applications—from infrastructure to residential and commercial buildings.

The prototype showcased at the Time Space Existence exhibition in Venice reflects a broader movement toward redefining housing in an era of ecological urgency. Its design, while addressing the immediate housing crisis serves as a strategic blueprint for integrating sustainability into mainstream construction. The site-specific cutout patterns, inspired by Venetian motifs highlight the meticulous design process, balancing aesthetics and practicality by reducing weight to accommodate the city's delicate infrastructure. By prioritising modularity, adaptability and low environmental impact, it offers a framework that can be tailored to diverse contexts, making it a versatile solution for regions grappling with rapid urbanisation and resource scarcity.

Beyond its conceptual value, Holcim has already validated the feasibility of biochar-infused construction materials through trials in countries like France, Spain, the UK and Greece. These practical tests demonstrate the readiness of this technology to transition from experimental stages to widespread application, heralding a new era of environmentally conscious construction practices.

Scaling such innovations from prototypes to pervasive practices is now the critical challenge. However, the USB represents a promising starting point; a vision of the built environment where progress and sustainability are not opposing forces but intertwined imperatives. The global construction industry, as exemplified by this collaboration, has the opportunity to redefine itself, transforming how we live while safeguarding the planet for future generations.