LSU professor advances the case for modern earthen buildings

Earthen buildings are nothing new—in fact, they’re one of the earliest forms of architecture in recorded history. Constructed primarily from soil, an earth structure utilizes various techniques and materials to remain upright: Combining mud and straw to make cob, building straight from sod, or adding stabilization through the inclusion of lime.

You might think we’ve left this method of building structures in the Neolithic era, but that’s not the case. Today it is estimated that anywhere from 8% to 10% of the world’s population live in earthen buildings, with the figure climbing to 20% to 25% for developing countries, according to a research paper published in the journal Building Research & Information.

Perhaps it is because earthen buildings are naturally fire- and termite-resistant, cost-effective, and structurally sound that they remain relevant centuries after their invention. Researchers continue to dive into the intricacies of earthen buildings and their potential when combined with binders and additive manufacturing.

Hai “Thomas” Lin, PhD, PE, an assistant professor of civil and environmental engineering at Louisiana State University, is one such researcher that has studied a unique approach to building earthen structures.

Mud Dauber Wasps Inspire Building 

A few years ago, Lin was watching mud dauber wasps build nests on his newly purchased home. As an assistant professor that worked on soil improvement, he was fascinated by the way mud daubers manipulate dirt to form intricate nests. Lin soon learned that “mud daubers are actually expert soil nest builders,” he says.

Mud daubers choose the soil for their nests through rigorous testing. To make working with soil easier to control, they manage its moisture content by repeatedly tapping the soil with their legs and jaws to compact it, then use air to harden it.

The mud daubers build their nests in clusters of tube-like cells rather than solid walls. With the mud dauber as his inspiration, Lin now aims to design homes made of 3D-printed soil. The mud dauber isn’t his only focus, however. 

Fungal Mycelium for Building Material Applications 

One of the first awards Lin received at LSU was titled “Enhancing Mycelium-Based Biocomposites for Novel Applications in Building Support and Design,” supported by the Louisiana Board of Regents. This research focused on fungal mycelium, the root-like structure of fungi, for building material applications.

Lin’s research team found that fungal mycelium can significantly enhance soil strength and waterproof the soil surface, highlighting its potential as a natural and sustainable solution for soil enhancement as a construction material.

His research into both fungal mycelium and mud dauber nests led Lin to think about their broader applications.

“The natural ingenuity of fungal mycelium and mud daubers inspired me to explore how they could modernize earthen building construction,” he says. “Mud dauber-inspired 3D soil printing can accelerate earthen building construction, making them more efficient and resilient. Fungal mycelium can act as a natural glue and water-repellent agent in printed earthen walls, significantly enhancing the strength, durability, and erosion resistance of printed soil structures.”

By integrating these bio-inspired approaches, Lin’s research envisions a new generation of sustainable, high-performance earthen buildings. 

CAREER Award Recipient 

Lin is the latest recipient of the National Science Foundation (NSF) CAREER Award. The CAREER program supports early-career faculty who demonstrate the potential to significantly impact their field through both research and education, while advancing the goals of their department or organization.

With an award prize of nearly $630,000, Lin will advance his research of mud dauber nests and the root systems of fungi to design 3D-printed soil for sustainable, durable, and cost-effective earthen buildings.

Some research has already shown how the modernization of earthen buildings through technology can be structurally effective.

Additive manufacturing, like 3D printing, has been investigated to reduce the often labor intensive and slow construction process of earthen buildings. Also, 3D printing technology can be used to create customized shapes and designs (mud dauber nests, anyone?). Some companies, like Italy-based WASP, have already managed to 3D print entire homes using local soil and stabilizers.

Modular construction via prefabricated panels or blocks made of earth are another means of innovating the classic earthen building. With the goal of shipping the modular pieces and assembling them on-site, construction time can be reduced. Lehm Ton Erde (“Loam Clay Earth”), a company based in Austria, produces prefabricated rammed earth walls.

The fabrication rests upon three essential ingredients: (1) a 50-meter formwork and from 35 to 45 centimeters in width, (2) a mobile conveyor belt to carry the earth into the formwork, and (3) a special machine to compact and flatten earth layers.

Binders are also typically used to improve the mechanical properties of earthen buildings. According to Lin, new binder alternatives are being investigated, including enzyme-based stabilization using the natural process of Microbial Induced Calcite Precipitation (MICP). The addition of natural fibers (straw, coconut husks) or synthetic fibers (polypropylene) to improve tensile strength and crack resistance has also been investigated. 

Earthen Building Benefits vs Stick or Steel 

Since earth remains a mechanically modest construction material, “it will never compete with concrete, steel, or even wood for being the substance of modern civil engineering works,” says Lin. However, earth material is perfectly suitable for one-, two-, or even three-story buildings.

Because earthen buildings can be made from locally sourced soil, they involve minimal industrial processing and reduce its embodied energy and carbon footprint.

As for thermal performance, earthen buildings have “excellent thermal mass,” according to Lin. The earthen walls can store heat during the day and release it at night, stabilizing indoor temperatures. Stick-built has poor thermal mass but good insulation when modern materials (fiberglass or spray foam) are used. Steel-frame has high thermal conductivity, leading to thermal bridging unless mitigated with advanced insulation systems.

Earthen buildings are naturally fire-resistant and impervious to rot or termites as well. However, stick-built has high fire risk and are susceptible to rot and pest infestations. Steel-frame buildings are fire-resistant but lose strength above 600°C and require additional protection against rust and corrosion. 

Research for Earthen Buildings in 5 to 10 Years  

So far, we’ve found that fungal mycelia can improve soil strength and erosion resistance, and that mud daubers can build very strong soil nests. The technology to build structures using these materials is still in the initial stages of development. Over the next five to 10 years, Lin’s research will focus on a few key areas.

Lin aims to investigate the long-term durability and performance of fungal mycelium-treated earthen walls under the environmental conditions of southern Louisiana, including exposure to moisture, temperature fluctuations, and mechanical stresses.

By adapting the construction techniques of mud daubers, he also plans to develop a 3D soil printing process that replicates their natural efficiency.

Lastly, he envisions constructing a one-story earthen building in Louisiana to serve as a real-world prototype. This will allow Lin and his students to test its structural integrity, durability, and suitability for wet climates.

In the end, earthen buildings may prove to be an ancient solution to a modern problem. In a world where we need housing more than ever, these novel methods could prove successful if we invest in them.