A comparative LCA of mid-rise residential building envelopes in Tehran: evaluating carbon emissions of conventional and carbon-absorbing materials in construction and operation

Building envelope materials play a crucial role in reducing life cycle carbon emissions and improving environmental sustainability. This study evaluates the life cycle environmental performance of four conventional wall systems used in Iran and an alternative hempcrete-based wall with carbon sequestration potential. Life cycle assessment (LCA) and building energy simulation were conducted using One Click LCA and DesignBuilder to quantify embodied and operational carbon over a 30-year service life. Results indicate that the LECA-based wall achieved the lowest life cycle carbon emissions (2,192 kg CO2e/m2), while the fired-clay wall showed the highest (2,303 kg CO2e/m2). Hempcrete reduced net emissions to 2,209 kg CO2e/m2 through biogenic carbon sequestration. Compared with the conventional fired-clay system, LECA and hempcrete reduced total life cycle carbon emissions by approximately 4.8% and 5.7%, respectively. These findings demonstrate that low-carbon and bio-based envelope materials can significantly improve the environmental performance of residential buildings in Iran’s hot-dry climate.