Thermal comfort and passive survivability in earthen buildings

Abstract

Earthen building materials have been regaining popularity due to their environmental, economic, and health advantages. Furthermore, given projected thermal survivability in the face of climate change, passive strategies that minimize use of fossil fuels for operational space conditioning are becoming increasingly necessary. Using the lens of passive survivability, this research investigates the abilities of four earthen wall assemblies (cob, light straw clay, unstabilized rammed earth, insulated unstabilized rammed earth) and three conventional assemblies (concrete masonry unit (CMU), insulated CMU, insulated wood frame) to provide adaptive thermal comfort in six distinct climates, with and without passive heating and cooling systems. Residential dwellings were evaluated through simulation with heat and moisture transport algorithms, showing that passive conditioning is especially beneficial with earth assemblies, bringing 25–70% of uncomfortable annual hours into the adaptive comfort zone, alongside strikingly lower diurnal temperature swings in all examined climates, and in all seasons, than conventional walls. Further investigation into the heat and moisture fluxes reveals that the thermal stability of the earth dwellings is provided in part by moisture sorption and evaporation. Together, for the first time, these results show that the thermal performance of earth assemblies can, with well-designed passive heating and cooling strategies, equal or outperform conventional assemblies in a range of U.S. climates, supporting their expanded inclusion in U.S. building codes. This research provides a novel contribution to the thermal performance optimization of earth construction, critically linking thermal and hygroscopic performance with passive design strategies such as shading, natural ventilation, and movable insulation.