Retrofitting suspended timber ground-floors; comparing aggregated and disaggregated evaluation methods

It is estimated that around 80% of UK dwellings have uninsulated ground floors, representing a significant heat loss mechanism in these buildings. In this research, an aggregated assessment of dwelling heat loss was made using the electric coheating test before and after a ground floor retrofit took place. Heat loss was reduced by 24% (43 ± 18 W/K) indicating that suspended timber ground floor retrofits could improve thermal comfort for occupants and contribute to government domestic energy efficiency policy targets. The findings indicate that disaggregated evaluation methods, such as spot heat flux density measurements, may overestimate the benefits of fabric retrofits. Aggregate methods may therefore be more appropriate tools with which to evaluate retrofits. The U-value improvement resulting from the suspended timber ground floor insulation retrofit, derived via aggregate measurement, was 0.55 W/m²K. Disaggregated spot heat flux density measurements indicated the improvement was 0.89 W/m2K. This research also indicates that Energy Performance Certificates, are unlikely to provide a reliable estimate of energy savings, because they rely on default assumptions for fabric U-Values and ventilation rates. This has implications for policy evaluations as well as householders, who may be excluded from financial support for retrofits.