The role of fabric performance in the seasonal overheating of dwellings

Airtightness and thermal conductance of the fabric play a key role in constructing low energy buildings. These two factors might minimise the building’s heating demand in winter but contribute to its overheating in summer. This study focused on a building using Insulated Concrete Formwork (ICF), a site-based Modern Methods of Construction (MMC). ICF walls consist of cast in situ concrete poured between two layers of Expanded Polystyrene (EPS) insulation. The walls can achieve very low U-values and high levels of airtightness. The overall aim was to investigate the resilience or vulnerability of the ICF to overheating. A whole building monitoring study was used to empirically investigate the impact of the ICF fabric performance and to validate the accuracy of Building Performance Simulation (BPS) predictions provided by two tools. The results indicate that the building was able to provide a stable internal environment. In addition, both tools were able to predict indoor temperatures in a consistent way. However, the outcome of the analysis highlighted the significance of selecting appropriate data in terms of weather, internal gains and occupant behaviour when assessing overheating and the importance of developing a methodology for model calibration against indoor air temperatures for overheating assessment.