The eco-refurbishment of a 19th century terraced house (energy, carbon and cost performance for current and future UK climates)

Much of the existing UK housing stock has a poor standard of energy performance and the residential sector currently accounts for around 25% of the country’s carbon dioxide (CO2) emissions. The eco-refurbishment of dwellings is a key action if the UK is to meet national targets for reducing carbon emissions, mitigating global warming and alleviating fuel poverty. Older properties tend to be the hardest to heat and the most difficult to refurbish, and this is particularly true for the UK’s five to six million terraced homes, many of which not only date back to the 19th century, but they represent early examples of mass urban living, hence they have strong cultural and architectural resonances. It is a significant challenge to the building industry, therefore, to sustainably renovate these buildings whilst maintaining their aesthetic character. This research analysed large amounts of monitoring data provided by the government’s ‘Retrofit for the Future’ programme for a 19th century, solid wall end-terraced house in Liverpool, England, in order to determine how the key features of the retrofit design would contribute to the improved energy performances of the refurbished houses. The aim of this renovation was to go beyond current UK thermal building regulations and to achieve the more exacting German Passivhaus standard. Analysing two years of extensive monitoring data revealed that the retrofitted house used 60% less energy and produced 76% fewer CO2 emissions than the estimated figures for a pre-refurbished house. Solar thermal panels provided over 61% of the hot water required in two year of occupancy. During the first year of occupancy the highest indoor air temperature was 26.5°C and indoor CO2 levels exceeded 1000PPM for 340 hours, or 11% of the occupied time. Using probabilistic UK future weather data and the dynamic thermal modelling software, DesignBuilder, the thermal performance of the house was simulated under different climate change probabilities with results indicating that the need to minimise over-heating, together with maintaining acceptable internal temperatures, will become increasingly important factors in retrofit design decision making. Finally, long term energy cost savings and carbon payback times for this case study were evaluated. The results of these calculations showed that the most favourable energy bill savings occurred when gas prices were rising – this gave a payback time of less than forty-three years. A carbon payback time of less than eight years means that there was no need for climate change sensitivity analysis of the model and the measures in the carbon payback time study. In addition, the Cost per Tonne of Carbon Saved (CTS) calculation showed that fabric measures, especially external wall insulation, are the most cost and carbon effective measures in the eco-retrofitted Liverpool terraced house