A case study of cob earth based building technique in Matagalpa, Nicaragua – LCA perspective and rate of adoption

Abstract: Cob is an earth based building technique that may be an alternative for the construction of new homes in developing countries. Earth based constructions techniques commonly used in the past, like adobe and wattle-and-daub, have increasingly been replaced by buildings using more processed materials commercially available such as bricks or concrete blocks. The cost of such commercial materials is often unreachable for a large part of the population in developing countries. Cob buildings could be an appropriate option in rural areas, where human labor is a less restricted resource compared to monetary capital, and most of the materials needed are locally available. The cob technique is based on a mixture of clay, sand, straw and water that enables the builder to combine different materials and to create a variety of shapes. A recently constructed cob building in Matagalpa, Nicaragua, was studied using screening LCA methodology applied to the construction phase, as well as by applying a diffusion of innovation framework (specifically the five perceived attributes of an innovation). Results regarding fossil CO2 emissions due to material production and material transportation were contrasted to an equivalent concrete block building. The highest contribution to CO2 emissions from the cob building was generated by paints and solvents, and bricks and tiles (cooked earth); whereas in the concrete building it was due to the concrete bricks and iron. According to this case study, cob building technique seems to have the potential to be an affordable option for rural housing in Nicaragua, and at the same time accountable for rather limited emissions of fossil CO2 emissions in its construction phase. At present, some obstacles to the use of cob technique are lack of examples for people to see and experience, and a general limited knowledge on how to work with cob technique.