Urban areas face escalating climate risks, resource scarcity, and environmental degradation, increasing the need for construction approaches that reduce life-cycle impacts while improving urban resilience and well-being. This critical review examines earthen construction and bio-based or bio-derived earthen composites through a multiscale perspective spanning material, building, and urban integration. It focuses on three interrelated dimensions: (a) the potential of earthen systems to reduce embodied carbon and support circular construction; (b) their contribution to passive performance through hygrothermal behaviour, including thermal inertia, moisture buffering, and indoor comfort; and (c) the barriers and enabling conditions affecting their adoption in contemporary urban contexts. The review distinguishes between unstabilized earth (UE), stabilized earth (SE), hybrid bio-based composites, and emerging techniques such as poured earth, and consolidates comparative ranges for compressive strength, thermal conductivity, dry density, and moisture-related behaviour. Evidence indicates that UE and SE occupy overlapping but differentiated performance domains, with stabilisation often improving strength, cohesion, and water resistance, while potentially increasing density, thermal conductivity, embodied impacts, and loss of reversibility. Earthen wall systems can also achieve competitive thermal transmittance without additional insulation, with typical U-values ranging from approximately 0.45 to 0.80 W/m 2 ·K and massive vernacular typologies reaching about 0.18 to 0.55 W/m 2 ·K. Beyond technical performance, the literature identifies regulatory gaps, certification and insurance barriers, fragmented supply chains, labour and training constraints, and persistent cultural perceptions as major obstacles to mainstream adoption. The review highlights opportunities to advance regenerative earthen design through low-impact stabilisation, prefabrication, digital manufacturing, performance-based validation, monitored demonstrators, and the integration of embodied-carbon and circularity metrics into urban policy and procurement. At the urban scale, earthen materials represent a promising but still insufficiently quantified field of climate-adaptation research, requiring further field evidence and coupled building-urban studies.
Cavada et al. (Wed,) studied this question.