The objective of the work is to evaluate the thermal behaviour and the environmental impact of selected building biowaste-based materials, mainly biomass from agrowaste. An evaluation of the state of the art of the materials used from waste or biomass in the construction of buildings is carried out. The selected building materials are based on data availability: hemp concrete, isotex, bricks with olive core flour (OCF), bricks with wheat straw (WS). Subsequently, thermal behaviour is evaluated as a function of decrement factor, time lag and as an application in the thermal envelope of a building. Finally, a life cycle assessment of each material is carried out, including the calculation of the following indicators: non-renewable energy, cumulative energy demand and global warming potential. Hemp concrete and isotex are the materials with better thermal behaviour (lower decrement factor and greater time lag) like conventional materials, but with lower environmental impact. Regarding bricks, mixtures of 8% OCF and 7%WS generate more stable indoor temperatures than 4% OCF and 3%WS. Compared with conventional materials, building materials with incorporated biomass have better thermal behaviour and allow the construction of buildings with lower life cycle impact. Graphical Abstract

Buildings are one of the systems that more energy consumed in the European Union. The study of the thermal envelope is interesting in order to reduce the energy losses. For that, a mathematical model able to predict the system response to external temperature variations is developed. With the mathematical model, different thermal envelope elements of a building based on the lag and the cushioning of the resultant wave can be characterized. In addition, it is important to analyse where the insulation is placed, because when the insulation is outside and the thermal mass is inside, the system produces a response with smooth temperature variations than when the insulation is inside. Therefore, placing the outside insulation generates more steady indoor temperatures, increasing the thermal comfort inside the building. To complete the mathematical model that allows predicting the temperature inside a building taking into account the solar inputs and the thermal inertia of the building. This study will help to establish the optimum design parameters in order to build sustainable and comfortable buildings. Furthermore, it will take one step forward in the construction of nearly Zero-Energy Buildings.

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