Hygrothermal Properties of Raw Earth Materials: A Literature Review

Raw earth historic and contemporary architectures are renowned for their good environmental properties of recyclability and low embodied energy along the production process. Earth massive walls are universally known to be able to regulate indoor thermal and hygroscopic conditions containing energy consumptions, creating comfortable interior spaces with a low carbon footprint. Therefore, earth buildings are de facto green buildings. As a result of this, some earthen technologies have been rediscovered and implemented to be adapted to the contemporary building production sector. Nevertheless, the diffusion of contemporary earthen architecture is decelerated by the lack of broadly accepted standards on its anti-seismic and thermal performance. Indeed, the former issue has been solved using high-tensile materials inside the walls or surface reinforcements on their sides to improve their flexural strength. The latter issue is related to the penalization of earth walls thermal behavior in current regulations, which tent to evaluate only the steady-state performance of building components, neglecting the benefit of heat storage and hygrothermal buffering effect provided by massive and porous envelopes as raw earth ones. In this paper, we show the results of a paper review concerning the hygrothermal performance of earthen materials for contemporary housing: great attention is given to the base materials which are used (inorganic soils, natural fibers, and mineral or recycled aggregates, chemical stabilizers), manufacturing procedures (when described), performed tests and final performances. Different earth techniques (adobe, cob, extruded bricks, rammed earth, compressed earth blocks, light earth) have been considered in order to highlight that earth material can act both as a conductive and insulating meterial depending on how it is implemented, adapting to several climate contests. The paper aims to summarize current progress in the improvement of thermal performance of raw earth traditional mixes, discuss the suitability of existing measurement protocols for hygroscopic and natural materials and provide guidance for further researches.