Elemental, the architecture firm led by Pritzker Prize-winner Alejandro Aravena, partnered with Holcim to present a timely project at the 2025 Venice Architecture Biennale: a prototype for a net-zero material basic service unit (USB), described by Aravena as the firm’s “most radical” design yet. The project builds on over 20 years of Elemental’s research in incremental housing and Holcim’s expertise in sustainable construction and materials.

The benefits of Aravena's incremental housing

In incremental housing, Elemental constructs the technically complex and expensive parts of a home—structural frame, roof, kitchen, bathroom, and essential service connections—while leaving space for residents to expand over time. This approach allows families to safely and gradually complete their homes, creating fully functional, higher-value houses. Over the past two decades, Elemental has implemented this model thousands of times across Latin America.

Housing as a process, not a product

In Venice, Elemental and Holcim take the concept further by presenting a compact structure that provides only the most essential services for living. Presented at the European Cultural Centre’s Time Space Existence exhibition, the prototype—described as a “structural sanitation unit”—measures 21 square meters across two floors, and accomodates infrastructure for a kitchen and bathroom. The structure is built from precast modular panels to enable rapid assembly. The panels feature cutouts that reduce weight and improve ventilation, making the design suitable for tropical climates in which incremental housing has so far been implemented.

The units are designed to meet urgent needs—shelter and sanitation—while remaining extendable by residents over time. A painted floorplan on the pavers beside the unit illustrate potential extensions, demonstrating how the incremental housing approach can evolve in practice. As Elemental notes, “Incremental design merely takes account of the fact that “housing” is a process, not a product, a verb rather than a noun.”

BioChar, a carbon-sequestering concrete
The project’s innovation extends beyond design: it is the world’s first use of Holcim’s carbon-sequestering concrete. This concrete mix incorporates biochar—a carbon-rich material produced from organic waste—into its formulation. Each kilogram of biochar used can prevent the release of up to three kilograms of CO₂, effectively turning the building into a carbon sink. Additionally, the concrete includes 100% recycled aggregates, further contributing to its sustainability.

The USB prototype at the Venice Biennale exemplifies how innovative design and sustainable materials can address urgent housing needs while mitigating environmental impact. By integrating biochar concrete and modular design principles, the project offers a scalable solution for resilient, carbon-neutral housing.