Holcim, in collaboration with the architecture studio ELEMENTAL, has unveiled the first full-scale prototype of a building made from biochar concrete. It promises affordability, fast construction, and scalability—while offering a more environmentally friendly alternative to conventional building materials. Innovations like this resonate strongly with initiatives such as Capacity2Transform, which promote green and creative approaches to sustainable development.
Using biochar also reduces emissions from cement production and, importantly, acts as a long-term carbon sink.
Biochar as a carbon sink
Biochar is a carbon-rich material produced by pyrolyzing biomass—such as wood or agricultural residues—through thermal decomposition in the absence of oxygen.
Why can we call it a carbon sink? Biomass naturally contains carbon that would normally be released back into the atmosphere as it decomposes or burns. Pyrolysis converts this biomass into biochar, which is chemically stable. In simple terms, biochar locks carbon away for the long term, preventing it from returning to the atmosphere as CO₂. It’s estimated that every kilogram of biochar can prevent the release of up to three kilograms of CO₂.
Biochar is primarily used in agriculture to improve soil fertility, but thanks to its properties, it is becoming increasingly popular in construction as well.
Better material properties and environmental benefits
Biochar can be added to concrete to create lightweight concrete with improved insulation and longer durability. Concrete mixed with biochar reduces heat transfer, improves thermal performance, and lowers energy consumption in buildings. It also significantly reduces the weight of the concrete while maintaining its strength.
Incorporating biochar into bricks and cement improves thermal insulation, moisture regulation, and overall material performance. Its porous structure helps regulate humidity, prevents mold growth, and improves indoor air quality. Its use also has a positive environmental impact, as cement production is extremely carbon-intensive. In fact, if the cement industry were a country, its emissions would be the third highest in the world—after the United States and China, according to faktaoklimatu.cz..
The first modular housing prototype with biochar concrete
At this year’s Biennale, the Swiss company Holcim—pioneers in sustainable construction—presented the first prototype of modular housing, the Basic Services Unit (USB). It is made from net-zero biochar concrete using 100% recycled aggregates. The project was developed in collaboration with Chilean architect Alejandro Aravena, a Pritzker Prize laureate.
The structure, described by ELEMENTAL as a “structural sanitary unit,” consists of a prefabricated concrete frame equipped with plumbing. The USB prototype has two floors that function as a service core: the lower level includes a kitchen sink, while the upper level contains a bathroom, washbasin, and toilet. Next to the structure, the outline of a house is marked—allowing a family to expand the home over time.
Building with biochar as a response to social, economic, and environmental challenges
Holcim and ELEMENTAL argue that this prototype could help address the growing demand for housing, its lack of affordability, and the need to consider environmental impacts. In the company’s press release, Alejandro Aravena stated: “Around one million people move into cities every week, and cities must be ready to receive them. If we don’t find solutions, it’s not that people won’t come—they will, but they’ll end up living in terrible conditions.”
The goal is to provide essential services—water, sewage, electricity, fire and earthquake resistance—without compromise, using modern and environmentally responsible materials. This mindset mirrors the values of Capacity2Transform, which encourages participants to rethink systems creatively while prioritizing environmental responsibility.
The 2022 IPCC report (AR6 – Climate Change 2022: Mitigation of Climate Change) also highlights biochar as a significant carbon removal technology, with a potential of up to 2.6 gigatons of CO₂ per year.
A material with potential—and challenges
Of course, the use of biochar in construction is still in its early stages. It shows great promise, but also brings challenges. Its properties vary depending on the input materials and production conditions, which are not yet standardized.
It’s also unclear what the optimal proportion of biochar should be—too much can weaken the material, while too little reduces its environmental benefits. Moreover, the carbon footprint depends on the energy source used for pyrolysis; if fossil fuels are used, the process can become more carbon-intensive.
Still, Holcim’s project demonstrates that decarbonizing construction can go hand in hand with addressing social needs such as affordable housing. The project is part of the company’s broader strategy focused on carbon-neutral and circular building solutions.
Innovations like biochar concrete illustrate exactly the kind of mindset that Capacity2Transform aims to cultivate. The project encourages participants to explore how green technologies and creative thinking can reshape traditional sectors — from construction to community development. Biochar-based building systems are a powerful example of how environmental responsibility, social impact, and design innovation can reinforce one another. They show that transforming systems is not only possible, but already happening, offering a concrete model for the type of future-oriented thinking C2T seeks to inspire.
Photos: Holcim
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