Conventional thermal insulation materials like mineral wools, polyurethane, and polystyrene foams are widely used in Europe, but their production significantly contributes to CO2 emissions, generating up to 6.9 times CO2. Additionally, these materials impede air circulation in buildings, leading to poor indoor air quality and discomfort. This project seeks to address the need for carbon-neutral or carbon-negative building materials that not only provide thermal insulation but also enhance indoor air quality through effective air filtration. The focus of this research is on developing lightweight indoor concrete blocks utilizing biochar, a carbon-rich material produced through pyrolysis. Biochar can sequester up to 2.6 times its own weight of CO2 while offering exceptional properties such as air filtration, acoustics, and thermal insulation. The project aims to maximize biochar content in concrete blocks to 50 to 75 vol% to achieve superior air filtration and thermal comfort while maintaining adequate mechanical performance. The methodology involves developing granulated biochar aggregates and combining them with low-carbon binders and biochar fines to develop lightweight, carbon-negative concrete blocks. Various mix designs, curing conditions, and additives will be explored to optimize the blocks' physical, mechanical, and durability properties. Advanced analytical techniques, including microstructural studies and multiscale modelling, will be employed to understand and validate the blocks' performance. This project has the potential to significantly advance sustainable building practices by developing a novel material that aligns with EU sustainability goals, the Paris Agreement, and the European Green Deal. By integrating biochar into building materials, this research offers an innovative approach to improving indoor air quality and energy efficiency, contributing to healthier and more sustainable living environments.