Building characteristics as determinants of propensity to high indoor summer temperatures in London dwellings

Cities are expected to experience an increasing risk of overheating due to climate change and the urban heat island phenomenon. Although external factors, such as urban morphology and greening, may influence the spatio-temporal variation of overheating risk, the individual building characteristics are also likely to be important. This paper presents the results of EnergyPlus dynamic thermal simulations of 3456 combinations of dwelling types and characteristics selected to represent the London domestic stock. Two Design Summer Year weather files were used to represent the current and future climate: the CIBSE 1984–2004 and a UKCP09 future weather file (50th percentile of external temperature, 2050s, medium emissions scenario). Appreciable variation between dwelling types but generally greater variation within dwelling type was found depending on such factors as orientation, surrounding buildings and insulation levels. Under the current climate, the insulation levels had considerable impact on indoor temperatures, with combined retrofitting of roof insulation and window upgrades reducing daytime living room temperatures during the warmest continuous 5-day period of modelling by, on average, 0.76 °C (%95C.I. 0.63, 0.89 °C) for mean temperature and 1.30 °C (%95C.I. 1.05, 1.54 °C) for maximum temperature. On the other hand, internally retrofitted walls and floors tended to increase daytime living room temperatures, with a combined effect of 0.46 °C (%95C.I. 0.33, 0.60 °C) increase in mean temperature and 0.71 °C (%95C.I. 0.47, 0.96) increase in maximum temperature. Within the context of a changing climate, knowledge of insulation characteristics after retrofitting is crucial for the accurate identification of dwellings with greatest overheating potential.