Beneficios y desafíos de revivir métodos constructivos tradicionales

Traditional construction materials present quantifiable environmental advantages over conventional industrialized materials. Rammed earth has an embodied carbon of 5-30 kg CO₂eq/m³ compared to 240-380 kg CO₂eq/m³ for reinforced concrete, according to the Inventory of Carbon and Energy (ICE) from the University of Bath (2019). Adobe presents values of 10-40 kg CO₂eq/m³, natural dry stone 8-15 kg CO₂eq/m³ (extraction and local transport only), and locally produced timber -700 to +110 kg CO₂eq/m³ (net negative balance when biogenic sequestration is accounted for). A 50 cm thick rammed earth wall, with a density of 1,800-2,000 kg/m³, provides a thermal transmittance of 1.5-2.0 W/m²·K and a thermal inertia capacity of 290-340 kJ/m²·K that buffers outdoor temperature fluctuations with a thermal lag of 10-14 hours, compared to 6-8 hours for a 25 cm brick wall with external insulation.

The empirical evidence on operational energy performance of buildings using traditional techniques is growing. A study by Serrano et al. (2016), published in Construction and Building Materials, monitored 12 contemporary rammed earth dwellings in southeastern Spain over 2 years and documented a heating and cooling energy consumption of 35-55 kWh/m²·year, 40-60% lower than the average for conventional dwellings in the same climate zone (90-120 kWh/m²·year). The key lies in thermal inertia: in climates with daily temperature swings exceeding 15 °C (common in inland Spain), earth walls stabilize indoor temperature between 22 and 26 °C without active conditioning for 7-8 months per year. The European CRAterre-ENSAG project (2020), which evaluated the hygrothermal behavior of 45 earthen buildings across 9 European countries, confirmed that earth walls naturally regulate indoor relative humidity between 40% and 65%, the optimal range for respiratory health, thanks to their moisture absorption-desorption capacity of 50-70 g/m² in 24-hour cycles.

The main barrier to the recovery of traditional construction methods is the absence of specific structural regulations in most European countries. In Spain, the CTE does not include earth walls (rammed earth, adobe, CEB) as a recognized construction system, requiring their use to be justified through article 5.1 of the CTE (alternative solutions) with equivalent technical documentation validated by the project's quality control. Only 4 European countries have specific national standards for earth construction: Germany (DIN 18942-100, 2018, for earth blocks), France (AFNOR XP P13-901 guides for CEB), Portugal (LNEC E0444 for rammed earth), and New Zealand (NZS 4298:1998, an international reference). The German standard DIN 18940 (2023), the most recent, establishes minimum compressive strength requirements of 1.5-5 N/mm² for earth walls depending on use category, compared to 10-50 N/mm² for conventional concrete. The strength is sufficient for buildings up to 3 stories with typical residential loads, but insufficient for uses with high imposed loads.

The seismic challenge limits application in risk zones. Unreinforced earth walls present a shear strength of 0.02-0.10 N/mm², far below that of reinforced concrete (0.5-2.0 N/mm²). However, recent research has developed reinforcement solutions: the inclusion of basalt fiber meshes or polymer geogrids in horizontal joints increases shear strength by 200-400% (Miccoli et al., 2015; Bulletin of Earthquake Engineering). In Peru, Technical Standard E.080 for Adobe (2017) allows reinforced adobe construction with welded wire mesh and cement mortar in zones of moderate seismicity, and a government program has reinforced 35,000 adobe dwellings with this technique between 2018 and 2023 at an average cost of 1,200 USD/dwelling. In Spain, the design seismic acceleration exceeds 0.12g in 30% of the territory (southern and southeastern peninsula), which requires mandatory reinforcement solutions for earth construction according to Eurocode 8. The homologation of these reinforcement solutions within the European regulatory framework is an essential step toward scaling earth construction.

The economic viability of traditional construction methods depends on their degree of industrialization. Compressed earth blocks (CEB), mechanically manufactured with hydraulic or manual presses, allow production of 300-800 blocks/hour with an industrial press at a unit cost of 0.15-0.40 EUR/block, competitive with ceramic brick (0.20-0.50 EUR/unit). The Spanish company Cannabric produces earth and hemp blocks with a compressive strength of 2.5-4 N/mm² and a thermal conductivity of 0.18 W/m·K, which eliminate the need for additional insulation in CTE climate zones C and D. Prefabricated rammed earth, developed by companies such as Lehm Ton Erde (Austria) and Pise Builders (Australia), uses rammed earth panels of 3-6 m² manufactured in the workshop and transported to site, reducing construction time by 40-60% compared to in-situ rammed earth and achieving a cost of 120-180 EUR/m² of finished wall, compared to 80-120 EUR/m² for a concrete block wall with ETICS insulation.

Life cycle cost (LCC) analysis favors traditional techniques when durability and maintenance are considered. A rammed earth wall has a documented service life of 500-1,000 years (inhabited rammed earth structures from the 12th century exist in Spain, such as the Alhambra in Granada) compared to the 50-100 year design life of reinforced concrete structures. Maintenance of a rammed earth wall is limited to surface rendering every 15-25 years at a cost of 5-10 EUR/m², while an ETICS system requires maintenance every 15-20 years at a cost of 20-40 EUR/m². A study by Fernandes et al. (2019), published in Journal of Building Engineering, calculated the 50-year LCC of a 120 m² single-family dwelling in the Portuguese Alentejo and found that rammed earth construction with a timber roof presented a total cost 12% lower than conventional brick construction with a concrete structure, when operational energy costs, maintenance, and component replacement were accounted for. The main barrier remains social perception: a CRAterre survey (2021) across 5 European countries revealed that 62% of potential homebuyers associate earth construction with poverty or precariousness, while only 23% perceive it as an ecological and premium option.

The shortage of skilled labor in traditional construction techniques constitutes a bottleneck for their scaling. In Spain, the Fundación Laboral de la Construcción (2023) identified 320 professionals with accredited training in earth construction (rammed earth builders, adobe builders, dry stone masons), compared to an estimated demand of 2,000-3,000 to serve the potential bioconstruction market. The art of dry stone walling was inscribed in 2018 on the UNESCO Representative List of the Intangible Cultural Heritage of Humanity, spurring training programs in Croatia, Cyprus, France, Greece, Italy, Slovenia, Spain, and Switzerland. In Spain, the Spanish Dry Stone Association has trained 450 people between 2019 and 2024 in courses of 40-120 hours, but the demand for restoration of 150,000 km of cataloged dry stone walls across Spain (data from the National Inventory, 2020) requires a much larger training scale.

Scaling perspectives depend on three converging factors. First, embodied carbon regulation: when Spain incorporates carbon footprint limits in the CTE (expected for 2026), earth, stone, and local timber materials will gain a quantifiable competitive advantage of 60-90% fewer emissions in modules A1-A3 compared to concrete. Second, regulated vocational training: France has included earth construction as a specialty within the Certificate of Professional Aptitude (CAP) for masonry since 2020, training 800 apprentices annually, a model that Spain could replicate through the SEPE professional certificates. Third, applied research: the European RE4 project (Horizon 2020, 2016-2020, 4.1 million EUR) developed prefabricated components of earth and recycled materials for industrialized construction, and demonstrated the viability of 4-story buildings with a mixed earth and timber structure that comply with the Eurocodes. The convergence of environmental regulation, vocational training, and industrialization of traditional techniques allows projecting that the market share of earth construction in Europe will grow from the current 0.3% to 2-5% by 2035, according to estimates from the European Rammed Earth Network (2023).