Data on Low and Zero Carbon housing in England and Wales
As discussed in the previous section England and Wales’ EPC data is divided into two metrics; the EER and EIR rating. As shown neither metric has a directly transferable relationship to heating load in KWh or CO2 emissions per m2. However, it is proposed that for the purpose of this analysis the EER metric is used as the primary focus, given that it takes a more rounded focus on overall energy costs for a property and is therefore a useful proxy for determining installation of energy saving measures. It is however recognised that the crudeness of this approach is open to potentially large errors in the SAP and RdSAP methodology, as explored by Kelly et al. (2012) Another important consideration is that although 13,630,487 (DECC, 2015a) EPCs have been lodged as of 30/06/2015, this represents just over half the building stock in England and Wales (DECC, 2014). Due to the fact that an EPC is only required during the sale, rent or change of tenure of a property; some dwellings that have undergone efficiency retrofit may remain excluded from these figures . DECC publish live tables on Energy Performance of Buildings Certificates, showing cumulative figures on EPC ratings as indicated in Figure 1.
Figure 1 EER rating as cumulative % of EPC certificates for England and Wales (DECC, 2015a) Given that EPCs are required only for new builds or those rent or sale, along with various energy initiatives, the EPC record does therefore not represent the entire housing stock in England and Wales. As part of their National Energy Efficiency Data-Framework (NEED) exercise, DECC have undertaken a number of weighting studies to redress this imbalance (DECC, 2014). Two datasets have been produces as part of the outcomes of the study • Public Use File (PUF): A sample of 49,815 records selected to be representative of the housing stock • End User Licence File (EUL): The end user licence file is a sample of 4 million records (4,086,448). A weighted adjustment was undertaken to the data sets to adjust for the inherent bias towards newer dwellings. For example, properties built since 2008 are more likely to be included in the dataset, and there are a higher proportion of more energy efficiency properties in the EPC data than in the England and Wales dwelling stock as a whole. 1.1.1 End user licence file (EUL)
The EUL data set attempted to take a representative sample of the England and Wales housing stock, from the wider EPC data (DECC, 2015b). It is considered that the EPC data contains a higher proportion of smaller modern flats and relatively fewer older detached properties, therefore a higher proportion of these were selected. Approximately half of all the EPC records were used in the analysis. To further correct for bias, a weighting variable has been included in the published EUL dataset. The weighting variable was determined using the variables stratified by region, property type and property age. The figures were then projected to reflect the national picture as of 2012 when the study was conducted, shown in Figure 2.
Figure 2 Estimate of EER % breakdown across total housing stock of England and Wales in EUL dataset including weighting rating for biases (DECC, 2015b) It is worth noting that any discussion of the energy performance of existing stock based on EPC data alone, is potentially open to these biases. Given that home owners or those in rented accommodation can undertake efficiency measures, without the need for an EPC assessment, it can be seen that not all efficiency measures will be captured by the published EPC statistics.
References DECC 2014. NEED: Anonymised dataset accompanying documentation. In: CHANGE, D. O. E. A. C. (ed.). London. DECC 2015a. D1 – All Dwellings in England & Wales – Number of Energy Performance Certificates lodged on the Register by Energy Efficiency Rating – in each Year/Quarter to 30/06/2015. London: Department of Energy and Climate Change. DECC 2015b. Lower Super Output Area: Energy Efficiency Band for Heat Map 2015. Department of Energy and Climate Change. KELLY, S., CRAWFORD-BROWN, D. & POLLITT, M. G. 2012. Building performance evaluation and certification in the UK: Is SAP fit for purpose? Renewable and Sustainable Energy Reviews, 16, 6861-6878.