Environmental Potential of Earth-Based Building Materials: Key Facts and Issues from a Life Cycle Assessment Perspective

The global challenge of large-scale climate change mitigation requires action also in the building and construction sector. From a life cycle perspective, and considering the mitigation timeframe, the issue of reducing embodied GHG emissions is gaining attention. Effective ways to reduce embodied GHG emissions have been proposed by the use of fast-growing, bio-based materials, due to carbon sequestered in the biomass. Another promising, yet largely under-explored option is to harness the environmental potentials and low embodied GHG emissions of earth-based materials for building construction. Earth construction dates back from 10,000 to 8000 BC and has been derived in many vernacular construction techniques. More recently, some earthen techniques have been modified, using stabilizers, mainly cement and lime, to increase strength and water stability. The objective of this article is to compare existing literature performed on the LCAs applied to various earthen construction techniques and seek for key factors. Transports as well as binder stabilizations are very influent on the results. Climate, nature of local soil, and geographical context are very influent on functionalities of buildings, mix design and transports, themselves influencing environmental impacts. According to design choices and local context, earthen construction is not always better than concrete. This means that no universal solution can be recommended with the LCA of an earthen wall. The solution has to be adapted to the local context. All references comparing walls material to conventional materials at the building scale, find better environmental performances of earthen walls compared to fired brick walls. However, a full comparison between earthen construction and conventional materials should account for the use phase: combining LCA models with thermal and durability models is a key research issue. Finally, it certainly would be useful to seek for solutions with best environmental performances in a local context, accounting for the nature of soil, the building's functional requirements as well as geographical and cultural specificities. Such an approach would ensure to lower environmental impacts but represents a drastic change in current construction practices. Whereas today building materials are standardized in order to fit with construction working practices, this paradigm shift would require to adapt construction working practices to the local material and context. As earthen construction is today, in many countries of the world, a re-emerging technique, and new professional practices are yet to be established, it seems possible to make this paradigm shift happen. Certainly, in the current context of the need to substantially reduce building-related GHG emissions, there is still strong potential in earth construction techniques for both research and building practice