Playing with Dirt: Rediscovering Earth as a Building Material

Long before architecture became an industry of systems, specifications and supply chains, it was something far more immediate. People built with what they could reach: stone from the hillside, timber from nearby forests, earth from the ground beneath their feet. These structures went beyond function, becoming inseparable from the places they occupied. Today, that relationship feels distant.

Modern construction is defined by materials manufactured, transported and assembled through highly industrialized processes. Concrete, steel and glass have enabled extraordinary advancements in scale and performance, but they also come with significant environmental costs. Together, they are among the largest contributors to global carbon emissions, forcing the design industry to confront a difficult question: what does it actually mean to build sustainably?

The answer is shifting.

Where sustainability once focused primarily on operational efficiency, the conversation has expanded to include embodied carbon — the emissions tied to extraction, production and transport — and circularity, a framework that challenges the traditional “take–make–dispose” model in favor of systems that keep materials in use and regenerate natural resources.

There is no singular solution waiting to be discovered. No material or technology can resolve the climate crisis on its own. Instead, the path forward is likely to be layered, iterative and, in some ways, uncomfortable, as it requires a fundamental reassessment of how we assign value to materials, processes and the built environment itself.

At RDG Planning & Design, that reassessment began with a simple but counterintuitive idea: instead of searching for something new, what if we looked backward?

A Material Wake-Up Call

The question wasn’t prompted by earth. It began with engineered stone. In 2024, Australia banned the sale and specification of the material following mounting evidence that its fabrication process was contributing to fatal lung disease in workers. While silica exposure has long been a known risk in masonry trades, the issue extended beyond dust alone. Many engineered products rely on proprietary resin binders, substances that are often more hazardous than the materials they are designed to replace.

For designers, the ban exposed a deeper problem: a growing disconnect between what materials promise and what they contain. Over the past decade, the industry has made meaningful progress toward transparency through tools like Health Product Declarations and red-list screening. But gaps remain. Critical information is frequently obscured under the label of “proprietary,” leaving designers to specify materials they cannot fully evaluate.

At the same time, construction itself has become increasingly complex. Walls are no longer singular elements but layered assemblies, each component performing a narrow, specialized function. Materials have become thinner, lighter and more efficient, at least by conventional definitions. But that efficiency comes with tradeoffs. These assemblies depend on multiple synthetic layers, tight interior–exterior separations and mechanical systems to maintain environmental control. They are designed to resist aging, to appear static and maintenance-free. In doing so, they distance buildings from both their material origins and their environmental context. 

Rammed earth challenges that framework.

Rediscovering Earth

Rammed earth is among the oldest known construction methods, with examples dating back more than 7,000 years. It appears across cultures and climates — from sections of the Great Wall of China to Moroccan kasbahs, Spanish fortifications and rural farmhouses in France. For centuries, it was a practical, intuitive way to build. Then it largely disappeared. 

The rise of industrial materials during the 19th and 20th centuries shifted construction toward standardized, mass-produced systems. Earth, by comparison, was seen as inconsistent, labor-intensive and outdated. Today, thankfully, that perception is beginning to change.

At its core, rammed earth is simple. Subsoil — a mixture of clay, silt, sand and aggregate — is compacted in layers within formwork to create dense, monolithic walls. When properly detailed, those walls offer a range of inherent benefits. They absorb and release moisture, helping regulate indoor humidity. Their mass stores heat, moderating temperature fluctuations. And when used without chemical stabilizers, they can return entirely to the ground at the end of their life cycle. Perhaps most importantly, they are local. Each wall reflects the geology of its site. Subtle variations in soil composition produce shifts in color and texture, creating layered surfaces that read as both structure and record, a physical imprint of place and process.

Yet even here, compromise often enters the equation. To improve durability and strength, builders frequently introduce stabilizers such as lime or Portland cement. While effective, these additives carry environmental consequences of their own. Cement production alone accounts for roughly 8% of global CO₂ emissions. Even so, rammed earth typically requires far less cement than conventional concrete. And ongoing research — including here at RDG — is exploring how to reduce or eliminate these binders entirely, pointing toward a future where the material’s performance aligns more closely with its ecological promise.

From Theory to Testing

At RDG, this exploration began in a lab in the Omaha office, with local soil and a willingness to experiment. Early samples were small and inconsistent — simple mixtures of clay, sand and aggregate, compacted by hand. But each iteration revealed something new. Moisture levels affected density. Clay content influenced cohesion. Aggregate size shaped both strength and surface character. Over time, trial and error gave way to a more deliberate process.

The team began systematically testing material ratios, compaction techniques and stabilizer content. Flat panels evolved into more complex forms, including curved and angular geometries that challenged assumptions about how the material could behave. A circular material strategy guided this work, linking performance testing with locally grounded partnerships. In collaboration with Endicott Brick, rejected bricks were processed into grog and used to replace sand in the mix, diverting waste while extending the life cycle of regional materials.

To evaluate structural performance, RDG partnered with TD2 Engineering to conduct compression testing. Industry benchmarks typically require rammed earth to achieve around 300 psi; multiple hand-tamped samples — stabilized with just 5% lime — reached 552 psi, nearly double the requirement. The results confirm not only strong structural performance, but also the viability of a locally sourced, circular approach to earth construction. 

The result was validating; it suggested that locally sourced earth, even without industrial-scale processes, could meet modern structural expectations. From there, the focus shifted. If strength were achievable, what could be reduced? Could Portland cement be minimized or replaced entirely? Could alternative binders — including emerging algae-based systems — provide comparable performance without the associated carbon impact?

At the same time, the team explored the material’s expressive potential. Iron oxide pigments were introduced to enhance natural stratification, emphasizing the layered construction process and expanding its architectural language.

The research eventually moved beyond the lab. Through a partnership with KANEKO’s Creative Camp, RDG translated its work into an educational experience for middle school students. Over the course of a week, participants were introduced to design principles through making. Each student began with an irregularly shaped base, developing a small-scale landscape through sketches and mockups. Using 3D-printed formwork, they constructed rammed earth walls by layering and compacting soil by hand.

Success depended on consistency, with each layer carefully placed and compressed. When the formwork was removed and the walls held their shape, the outcome was immediate and tangible. Structure was no longer abstract; it was something they had created.

As individual pieces came together into a larger installation, the project reframed perception, helping the students understand how what began as dirt could become material.

Confronting the Challenges

Despite its promise, rammed earth is not without obstacles, and technical concerns remain. The material performs well in compression but has limited tensile strength, often requiring hybrid systems to meet broader structural demands. Durability in certain climates — particularly those with high moisture or freeze–thaw cycles — continues to be studied, with plant-based sealants offering potential but not yet fully proven solutions.

Practical considerations also play a role. While the raw material itself is inexpensive, the process can be labor-intensive, requiring time, skill and carefully constructed formwork. Efforts to introduce prefabrication and modular approaches may help address these constraints. But the most persistent challenge may be cultural. Rammed earth doesn’t align with prevailing expectations of precision and permanence. Its surfaces shift, crack and patina over time. Rather than resisting change, the material records it. In a construction culture that often prioritizes uniformity and control, that variability can be difficult to accept.

And yet, it is precisely these qualities that make rammed earth relevant. As the unintended consequences of industrial progress, particularly climate change, become more visible, the assumptions that have guided modern construction are being reexamined. In that context, earth offers a different way of thinking about buildings and their relationship to the environment. Across the profession, architects, engineers and researchers are testing how low-impact, locally sourced materials can meet contemporary expectations for performance, durability and design.

Here at RDG, this work continues. What began as an experiment with dirt has become a broader inquiry into how architecture can reconnect with the systems it depends on: ecological, material and cultural. Because in the end, the question isn’t whether earth can perform — it’s whether we are willing to rethink what performance means.

Reference note: This article draws in part on concepts outlined in the Manual of Biogenic House Sections by LTL Architects.