Introduction to Sustainability and Ancestral Construction Techniques

This introduction to sustainability and ancestral construction techniques begins with a fundamental fact: raw earth is the most widely used building material in human history. Approximately 30% of the world's population (2.4 billion people) currently lives in earth buildings (UN-Habitat, 2023), and the oldest surviving earth structures date back more than 8,000 years (Catalhoyuk, Turkey). Ancestral construction techniques — adobe, rammed earth, quincha, dry stone, bahareque, cob — represent solutions optimized over millennia for the climatic, seismic and material conditions of each region, and they share a common principle: the use of local, non-industrially processed materials, with a production energy consumption of 0.5-5 MJ/kg compared to 3-30 MJ/kg for industrialized materials (concrete, steel, glass).

Contemporary research on these techniques is led by the CRAterre laboratory (Centre de Recherche et d'Application — Terre, ENSAG Grenoble, founded in 1979), which has documented more than 150 earth construction techniques worldwide. UNESCO has recognized 100+ World Heritage Sites built with earth techniques: the Great Mosque of Djenne (Mali, adobe, 1907 on a 13th-century structure, 4,500 m2 — the largest earth building in the world), the Alhambra of Granada (rammed earth, 13th-14th centuries), the ksour of the Sahara (Berber earth architecture), the Fujian tulou (China, circular rammed earth: diameter of 30-70 m, 3-5 stories, capacity for 300-800 inhabitants). These buildings demonstrate durabilities of 200-1,000 years with periodic maintenance — a performance that contemporary industrialized construction can scarcely match.

Adobe (from the Arabic al-tub: brick) consists of blocks of clay-rich soil + sand + water + plant fiber (straw, hemp) molded and sun-dried for 15-30 days. Adobe properties vary with soil composition: density 1,200-1,800 kg/m3, compressive strength 1-3 MPa (sufficient for 1-3 story buildings), thermal conductivity 0.50-0.80 W/mK (similar to solid brick but with greater thermal mass), specific heat 800-1,000 J/kgK. A 40 cm adobe wall provides a thermal time lag of 8-12 hours — ideal for climates with a diurnal/nocturnal temperature amplitude exceeding 15 degrees C (continental and desert climates), because it stores daytime heat and releases it during the cool night.

Rammed earth (tapial) is clay-rich soil at 10-15% moisture content compacted in formwork to a density of 1,800-2,100 kg/m3, achieving compressive strength of 1-4 MPa (unstabilized) and 5-10 MPa (stabilized with 5-8% Portland cement or lime). The thermal conductivity of rammed earth is 0.70-1.10 W/mK, and its thermal mass is the highest of all earth techniques (1,800-2,100 kJ/m3K). The embodied carbon of unstabilized rammed earth is 5-20 kgCO2/m3 — 95-98% lower than that of reinforced concrete (300-500 kgCO2/m3). Cement-stabilized rammed earth (CSRE) increases to 30-80 kgCO2/m3 — still 80-90% lower than concrete. The Ricola Krauterzentrum project (Laufen, Switzerland, 2014, Herzog and de Meuron) is an industrial warehouse of 5,000 m2 with unstabilized rammed earth walls of 40 cm rising to 11 m in height, demonstrating that contemporary rammed earth achieves architecturally significant dimensions.

Quincha (also bahareque, wattle and daub) is a lightweight frame construction system: load-bearing structure of wood or cane (guadua, bamboo), infill of mud with fiber and a lime or mud render finish. Its wall weight per square meter is 80-150 kg/m2 (compared to 400-800 kg/m2 for rammed earth), which reduces seismic loads on the foundations by 60-80%. Quincha has demonstrated exceptional seismic performance: during the Pisco earthquake (Peru, 2007, Mw 8.0), heritage quincha buildings restored by PUCP (Pontificia Universidad Catolica del Peru) with polymer mesh reinforcement sustained minimal damage, while unreinforced masonry buildings collapsed. Research by Blondet et al. (2011) documented that reinforced quincha withstands seismic accelerations of 0.3-0.5g without collapse.

Dry stone is the oldest and most durable construction technique: natural stone walls without mortar, with pieces selected and fitted together by gravity and friction. The dry stone walls of Machu Picchu (Peru, 15th century) withstand earthquakes exceeding magnitude 7 on the Richter scale thanks to the flexibility of their mortarless joints. In Europe, dry stone walling is protected as UNESCO heritage (2018: "Art of dry stone walling, knowledge and techniques") across 8 countries (Croatia, Cyprus, France, Greece, Italy, Slovenia, Spain, Switzerland). The thermal properties of a 60 cm dry stone wall (conductivity: 1.5-3.0 W/mK) are inferior to those of rammed earth, but its thermal mass (2,200-2,600 kg/m3) provides a thermal time lag of 10-15 hours. Its documented service life exceeds 500 years without significant maintenance. Other ancestral techniques with contemporary relevance include: cob (a mixture of earth, straw and water applied by hand without formwork: 15th-century cob buildings in Devon, England, remain inhabited), the Nubian vault (compressed earth without centering, documented since 3,000 BCE in Egypt, revived by Hassan Fathy in New Gourna in 1946), and palm and thatch roofing (thermal conductivity: 0.05-0.09 W/mK — comparable to EPS, with the added advantage of being biodegradable and renewable).

The integration of ancestral construction techniques with contemporary technology makes it possible to combine the thermal, environmental and cultural properties of traditional materials with current performance and safety standards. Integration strategies include: (1) rammed earth + external insulation — a 30 cm rammed earth wall with 10 cm of wood fiber insulation on the exterior achieves a transmittance of U = 0.20 W/m2K (Passivhaus level) with interior thermal mass of 540 kJ/m2K; (2) adobe + seismic reinforcement — biaxial geogrid mesh embedded in the render (PUCP technique) increases the seismic resistance of adobe by 300-400%, at a cost of 5-8 EUR/m2; (3) timber/steel frame + earth infill — the load-bearing structure meets modern seismic building codes, while the earth infills provide thermal mass, hygroscopic regulation and a traditional aesthetic.

The CEB (Compressed Earth Block) is the industrialized evolution of adobe: soil with 5-10% cement mechanically compressed at 10-20 MPa, achieving compressive strength of 5-15 MPa (comparable to fired clay brick) and dimensional tolerances of +/-1 mm. The cost of CEB is 0.15-0.30 EUR/unit (local production with manual press: 500-1,000 blocks/day) or 0.30-0.60 EUR/unit (automated hydraulic press: 3,000-5,000 blocks/day). Digital soil mapping (grain-size analysis + Atterberg limits + organic matter content) enables identification of soils suitable for construction in any locality, optimizing the composition without extensive testing. Notable contemporary projects include: the Mapungubwe Interpretation Centre (South Africa, 2009, Peter Rich Architects, CEB vault without steel structure: Aga Khan Award 2013), the Thread Cultural Center (Senegal, 2015, Toshiko Mori: bamboo structure + local laterite walls), and the 5-story rammed earth tower (Weilburg, Germany, 1828: the tallest earth building in Europe, continuously inhabited for 196 years). Building regulations for earth construction vary by country: France (regles professionnelles de construction en terre crue, 2018), Germany (DIN 18945-18948: Lehmbaustoffe), New Zealand (NZS 4298:1998: Materials and Workmanship for Earth Buildings), Peru (NTE E.080: Adobe). Spain lacks a specific standard, although the CTE permits its use through recognized documents and alternative solutions with technical justification.