This paper highlights the impact of environmental conditions on cob buildings. Different factors such as wall thickness, material permeability and interactions between moisture and heat fluxes can all have significant effects on the performance and durability of cob buildings. An experimental and modeling-based study was conducted on the hygrothermal characterization of cob building materials, which were obtained by mixing earth and fibers. Two types of cob materials that can be used as insulation and to form structural materials in buildings were tested. The effect of outside temperature on adsorption isotherms was investigated for both materials. The experimental data were fitted using the GAB model, after which a new correlation of water content correlation was proposed. Three specific configurations were investigated in which cob material was subjected to moisture transfer and a zero, positive or negative temperature gradient. Based on the resulting measurements, a high coupling effect between heat and moisture transfer inside the structural material was analyzed. A comparison of the experimental and modeling results demonstrated the satisfactory correlation and reliability of the developed model. Simulations were carried out for various wall thicknesses, in order to assess the effect of heat and moisture transfer on water content. The three scenarios were simulated and distributions of water content inside the walls were determined. The results show that the wall thickness of cob buildings and the direction of heat and moisture fluxes affect water content distribution in the structure. A greater thickness of the cob wall leads to higher water content, but this relationship reverses when the heat and moisture fluxes move in the same direction.

Faced with the current challenges of the energy transition and the quest for sustainable materials, biobased materials are attracting growing interest for their environmental and thermal properties. Cob is well known for regulating humidity and improving thermal comfort in buildings. A building’s thermal inertia can be increased by integrating phase-change materials (PCMs), enabling energy storage. This study explores the integration of microencapsulated PCMs into biobased materials considering realistic environmental conditions during experimental tests. The results show a homogeneous thermal distribution with low temperature variation at different locations. The relative humidity results confirm a one-dimensional thermal and hygroscopic distribution. The material with PCMs exhibits better thermal regulation. It retains more heat on the outside and reduces indoor temperature variations, improving thermal insulation. Measurements show that PCM integration contributes to reducing wall thermal conductivity and increases its thermal capacity, reaching 2.6 times during phase transition. The simulation is conducted with real 96 h Normandy climate data (January and August) for conventional and biobased walls incorporating PCMs. The results show that winter heat losses are highest for conventional walls (−44.08 kWh/m²), low for cob walls (−24.17 kWh/m²), and lowest for cob walls with PCMs (−13.17 kWh/m²). In summer, all walls exhibit the lowest heat gain, while adding PCMs stabilizes heat flux, reducing peak summer heat flux from 150 W/m² to 50 W/m². The results show that the addition of PCMs significantly improves thermal and hygroscopic performance.

Biosourced materials made of a combination of raw earth and fibers are attracting increasing interest for low-carbon construction due to their reduced environmental impact and good thermal and hygric performance. This study investigates several soil–fiber composites selected and formulated at different densities to assess their thermal conductivity, enabling the selection of two complementary materials: a structural earthen mix and a lightweight insulating mix. Experimental measurements were taken under controlled conditions and used to characterize heat and moisture fluxes, and numerical calculations were carried out to evaluate the performance of single and double-layer wall configurations. The results showed that an increase in thermal gradients accelerates vapor migration and alters the internal distribution of moisture. The evaluation of wall configurations demonstrated that placing the earthen insulating layer externally optimizes thermal fluxes and eliminates condensation risks at the interface between materials, while internal insulation can be sensitive to hygrothermal gradients and prone to moisture accumulation. The combined experimental–numerical approach provides new insights into high-performance designs of bio-based earthen envelopes, establishing guidelines for minimizing moisture-related risks in low-carbon building systems.

Earth-based materials are promising candidates for balancing thermal performance, hygrothermal regulation, and environmental sustainability. The objective of this study is to evaluate and compare the hygrothermal behavior of two earthen materials, structural cob and lightweight insulating earth, against conventional reference concrete, taking into account not only their insulating properties but also their ability to regulate coupled heat and moisture transfers. Experimental tests show a significantly higher hygroscopic buffering capacity for earth-based materials, with an MBV of 2.23 g/(m²∙%RH) for the structural material and 1.21 g/(m²∙%RH) for the insulation material, compared to less than 0.5 g/(m²∙%RH) for concrete. The sorption isotherms confirm distinct water storage behaviors, with an average sensitivity to relative humidity of 10.47% for the insulation material, compared to 3.8% for concrete and 2.25% for the structural material, in addition to an average reduction of 26% in the adsorption capacity between 23 °C and 45 °C for both earthen materials. Coupled heat–moisture simulations in COMSOL quantitatively demonstrate the hygrothermal superiority of bio-based materials over conventional concrete, as concrete promotes interstitial moisture accumulation due to its low vapor permeability. The parametric sensitivity analysis highlights the effect of hygrothermal properties, where diffusivity controls transport kinetics and sorption governs water storage, while thermal conductivity modulates the spatial redistribution of thermo-hygric fields. The next and final step made it possible to link the phenomena observed at the material scale to the actual energy performance of the building, confirming the potential of the double-wall cob + lightweight earth system to reduce heating and cooling requirements and maintain stable indoor comfort, where the annual heating demand is reduced by approximately 24% compared to the conventional prototype.

La transition vers une construction durable et écoénergétique est un enjeu clé dans la lutte contre le changement climatique et la réduction de l’empreinte carbone du secteur du bâtiment. Pour répondre à ces défis, l’utilisation de matériaux biosourcés représente une alternative prometteuse en raison de leur faible impact environnemental et de leurs propriétés naturelles de régulation thermique et hygrométrique. Cependant, ces matériaux présentent encore des limites en matière de performance énergétique et de stabilité hygrothermique, nécessitant une optimisation pour leur intégration à grande échelle dans les constructions modernes. L’une des approches les plus innovantes dans ce domaine consiste à coupler ces matériaux avec des matériaux à changement de phase (MCP), capables d’améliorer leur inertie thermique et de stabiliser les variations d’humidité. Dans cette étude, deux types de matériaux biosourcés ont été sélectionnés et analysés : la terre allégée, utilisée comme isolant, et la bauge ; un matériau porteur. Une caractérisation expérimentale a été menée pour évaluer leurs propriétés thermiques et hygrométriques, révélant des différences notables entre ces deux matériaux. Alors que la terre allégée se distingue par sa faible conductivité thermique, assurant une bonne isolation thermique, la bauge possède une capacité de régulation hygrométrique permettant une meilleure gestion de l’humidité. L’étude des transferts couplés de chaleur et d’humidité a mis en évidence l’importance des flux thermiques et hygriques dans la performance énergétique des parois. Un modèle numérique a été développé pour simuler ces transferts dans différentes configurations de murs et valider les observations expérimentales. Les simulations ont montré que l’isolation intérieure entraîne une perte d’énergie plus importante que l’isolation extérieure, bien qu’elle permette un meilleur stockage hygrométrique, contribuant ainsi à la stabilité de l’humidité intérieure et à la réduction des risques de condensation. L’ajout de MCP dans la bauge a permis de modifier ses propriétés thermiques et hygrométriques. Les MCP ont contribué à réduire la conductivité thermique et à augmenter la capacité de stockage de chaleur, améliorant ainsi l’inertie thermique des parois. En parallèle, ils jouent un rôle clé dans l’absorption et la restitution de l’humidité, ce qui limite les fluctuations hygrométriques et améliore le confort intérieur. L’évaluation des performances des murs intégrant des MCP a révélé que leur composition et disposition influencent directement leur efficacité énergétique. Trois configurations de murs ont été étudiées. La première configuration, composée uniquement d’une couche structurelle et d’une isolation, présente les performances les plus limitées en matière de régulation thermique et hygrométrique. La seconde configuration intègre 20 % de MCP dans la couche structurelle, permettant ainsi une amélioration significative de l’absorption et de la désorption de l’humidité. Enfin, la troisième configuration associe un panneau Energain avec MCP, une couche structurelle et une isolation, ce qui permet une réduction efficace des fluctuations thermiques et hygrométriques. Cette dernière solution s’est révélée trois fois plus performante que la première en termes de stabilisation thermique. En combinant deux approches expérimentale et modélisation numérique, cette recherche contribue à l’amélioration des stratégies de construction biosourcée, en proposant des solutions innovantes pour renforcer l’efficacité énergétique des bâtiments tout en favorisant une construction plus durable et respectueuse de l’environnement.