School Renovation Impact on IAQ and Embodied Carbon: A Comparative Field Study with Statistical and LCA Insights

Indoor air quality (IAQ) in schools is directly linked to student health, comfort, and performance, while renovation strategies are increasingly assessed for their embodied carbon impacts alongside energy savings. However, little is known about how renovation affects both IAQ and embodied emissions in real school settings. This study hypothesized that renovation improves thermal stability but may not ensure compliance with IAQ standards, while introducing additional embodied carbon from new materials. To test this, two architecturally identical Lithuanian schools, one renovated, one non-renovated, were compared during the transition from heating to cooling season. IAQ monitoring focused on carbon dioxide (CO2), temperature, and relative humidity, and a life cycle assessment (LCA) was used to evaluate the additional embodied carbon of renovation materials, since energy-focused upgrades like insulation and new windows can improve indoor comfort but also increase material-related emissions. Results showed that renovation improved temperature stability and reduced sensitivity to outdoor conditions, but both schools frequently exceeded recommended CO2 thresholds during lessons. The LCA showed notable embodied carbon impacts from façade insulation and window replacement (A1-A3 stages), highlighting a trade-off between material use and comfort gains, though long-term operational savings may offset these initial emissions over the building service life. The results underline the importance of renovation that brings together thermal comfort and CO2 performance and embodied carbon reduction to create both healthy and sustainable learning environments.