CO2 emissions in 2018 reached the highest level in the human history. Architecture design has become an important tool to deal with current environmental problems; the use of non toxic materials and the energy consumption control in buildings life-cycle are strategies that significantly reduce anthropogenic emissions. Biochar, a biomass charred through pyrolysis, allows the capture and storage of carbon. Charcoal stores 50% of its C content for centuries, while biomass combustion and natural decomposition release ~90% of C within 5-10 years. In this research, biochar is used as a building material, in addition to a lime-hemp insulating plaster. Possible improvements of the mixture in different experimental fields are reported, such as mechanical strength or humidity control.