What if there was a building material that was easily obtainable, environmentally sustainable, and inexpensive?
Well, there is. Just look down—you’re literally standing on it. Earth.
Soil as a building material is utilized in sun-dried mud brick (adobe) structures, rammed-earth walls, wattle and daub buildings, and in a variety of other construction techniques that vary from culture to culture and region to region. According to the United Nations, an estimated 30 percent of the world’s population lives in houses made of earth, and earth remains a prevalent building material in many parts of Africa, Asia, and Central and South America. The UNESCO World Heritage List includes more than 200 earthen sites.
Although this seemingly modest material has been used in construction for millennia, people often perceive it as something found solely in developing countries, as a local form of architecture. This is far from the truth. You can find earthen structures of almost every architectural type throughout the world, ranging from ancient archaeological sites to modern buildings. You see earth in large complexes and historic centers, in individual buildings, and in the form of decorated surfaces.
Consider the beautiful neighborhoods of Santa Fe, New Mexico, old and new, made of mud brick. The oldest public building in the United States still in use is the Palace of the Governors in Santa Fe, built in 1610 and today part of the New Mexico History Museum. The walls of the Alhambra Palace in Granada, Spain, are largely constructed of rammed earth; the palace’s name, from the Arabic Al Hamra, meaning red, is in reference to the color reflected by earthen walls at sunset. In Mali, the Old Towns of Djenné, including the Great Mosque, are made from earth formed into djenné ferey—cylindrical bricks shaped by hand—and the transmission of knowledge for this construction method is passed from father to son guided by the bareyton, a mason’s guild.
What about Earthquakes?
Earthquakes—especially the 2003 quake in the ancient Iranian city of Bam that destroyed more than 70 percent of the earthen buildings and killed much of the population—have earned earthen structures the reputation of being structurally unsound. But many of the fallen structures had previously survived for more than 500 years in this earthquake-prone region. Placed on the UNESCO List of Heritage in Danger the following year, Bam has since been the subject of a restoration project that is still ongoing.
It’s also important to note that modern materials such as concrete, which in many developing economies signifies progress, can also fail, as demonstrated by the 1971 collapse of the brand-new Sylmar hospital during the San Fernando, California, earthquake; the collapse of the Ponte Morandi bridge in Genoa in 2018; and just last year, the Champlain Towers South condominium in Surfside, Florida. Understanding the materials and construction techniques, as well as conducting ongoing maintenance, are key to ensuring a building’s longevity and structural integrity, no matter its building materials.
To address seismic safety in historic earthen structures, the Getty Conservation Institute (GCI), in a project with the Ministerio de Cultura del Perú, the Escuela de Ciencias e Ingeniería of the Pontificia Universidad Católica del Perú, and the University of Minho, has developed an innovative seismic retrofitting approach. (The Seismic Retrofitting Project is a component of GCI’s Earthen Architecture Initiative, an effort to support the field of earthen architecture conservation through laboratory research, field projects, training, conferences, and publications.) This new approach combines traditional construction techniques and materials with high-tech analysis—all to design and test easy-to-implement seismic retrofitting and maintenance programs that will improve the structural performance and safety of earthen buildings while minimizing loss of historic building material.
The seismic retrofitting of the small 17th-century Church of Santiago Apóstol in Kuñotambo in the Peruvian Andes, one of four case studies for this project, has been completed, and the focus now turns to a much larger structure, the cathedral in Ica, Peru, constructed in 1759. The new seismic retrofitting approach is intended to be widely applicable across Latin America—where the majority of historic structures are constructed of earthen materials—and detailed information on it is available through a series of free downloadable publications in English and Spanish.