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This paper aims to focus on the assessment of a domestic property's energy performance status by a domestic energy assessor (DEA), to ascertain the possible underlying reasons for variability in the results of Energy Performance Certificates (EPCs). By variability, the authors mean discrepancies in assessment between different DEAs on similar properties. This is important because the uses for the EPC have been extended beyond their original function as an asset rating system, to include themes encompassing building policy decisions, building performance and the distribution of incentives and grants. Consequently, inaccuracies in EPC reporting will have a greater impact than may have been the case at the outset.

A case study approach involving the conducting of semi-structured interviews with 20 practicing DEAs was carried out, with transcribed recordings of the interview material subjected to thematic analysis. This formed part of a wider mixed methods study.

The results identify a wide range of underlying reasons for variability driven by issues in both practice and process, including conflicts of interests, the EPC auditing process, the default inputting of missing data by RdSAP where information may not be available/discoverable by the DEA, the quality and perception of EPCs and DEA training and experience.

The sample size of 20 is by definition limiting, and it is possible that different results would have been obtained from a different sample. Although thematic saturation from the analysis of the responses on the key question of whether EPCs are considered variable does mitigate this. The respondents were all in possession of five years or more experience and of carrying out EPCs for different purposes. Less experienced DEAs may inevitably have responded to questions differently. The thematic analysis gives the researcher control over the presentation of the results, and it is noted that this creates a potential for bias. The researcher is immersed in the world of construction and property, with regular contact with DEAs and EPCs, which may influence the perspective of the results.

The research identifies risks to the accuracy of EPCs. To this end, and with the specific research findings in mind, this research may be of interest to construction professionals with respect to EPC practice and procurement, to the Accrediting Bodies who audit EPCs, to the creators of RdSAP with respect to automated EPC inputs, to academics either at face value or for use in further research and to policy makers who may wish to consider RdSAP data in future with qualifiers or margins of error, or may even look to review the EPC as the instrument of choice for some applications.

There is much literature analysing the shortcomings and nuances of RdSAP results, and the software model that generates the EPC, but only very limited literature extending the discussion about RdSAP to its operator: the DEA. At the time of writing, there is no literature focusing directly on the DEA and its role within the EPC production process. Their role is more important now, given the expanding use of EPCs, and increased reliance on EPC data.

Climate change is one of the most significant challenges of our time. The existing housing stock is a crucial component in achieving international and national climate change targets through energy efficiency improvements. The private rental sector incorporates some of the worst performing housing. To address this, the UK has implemented the minimum energy efficiency standard, based on the energy performance certificate rating. However, the energy performance certificate has a number of criticisms in the UK and across the EU. This viewpoints paper discusses the primary criticisms of the EPC and whether these undermine the minimum energy efficiency standard.

This viewpoint paper draws on the recent work across academic, government and professional literature to develop a critique of the energy performance certificate and its underlying methodology as a basis on which to form the minimum energy efficiency standard.

The paper concludes that based on the current form of the energy performance certificate in the UK, the minimum energy efficiency standard is likely to unfairly advantage some landlords and penalise others. This has implications for landlords, tenants and the wider housing stock.

This paper presents a discussion of the new minimum energy efficiency standard based on the limitations of the energy performance certificate. It has implications for policymakers, researchers and practitioners in the private rental sector.

The purpose of this paper is to provide a detailed appraisal of the quality of domestic retrofits.

This paper presents the results of technical surveys on 51 retrofits undertaken before, during and after the retrofits.

Failures are observed to be endemic and characterised into five themes: 72 per cent showed moisture issues pre-retrofit, 68 per cent had moisture risks post-retrofit, 62 per cent did not adopt a whole house approach, 16 per cent showed inadequate quality assurance protocols and 64 per cent showed evidence of insufficient design detailing. Each theme is further subcategorised with a view to identifying implications for future policy.

The findings suggest the 10 per cent Ofgem retrofit failure rates predictions are an underestimate and so there may be a need for additional investigations to understand the trend across the UK.

Recommendations to reduce the failure rates may include making changes to the current inspection regime, widening understanding among installers; providing standard repeatable designs for repeated features; and empowering occupants to trigger inspections.

The sample is representative of a substantial proportion of the homes in the UK suggesting that retrofit quality may in many instances be below the required standards.

Risks of moisture issues and underperformance in domestic retrofit are a concern for government industry and households. This research shows that many installation failures are the result of not implementing existing guidelines and a change to the enforcement of standards may be needed to enact a fundamental change in installer practice and process control.

The purpose of this paper is to identify the impact of traditionally unmonitored energy sources and sinks on assessment of the as-built thermal performance of occupied homes. The analysis aims to demonstrate the potential scale of uncertainties introduced in a heat balance estimation of the heat transfer coefficient (HTC) when using in-use monitored data.

Energy flows for two UK homes – one a 1930s dwelling with high heat loss, the second a higher-performing 2014-built home – are predicted using the UK Government’s standard assessment procedure (SAP) and visualised using Sankey diagrams. Selected modelled energy flows are used as inputs in a quasi-steady state heat balance to calculate in-use HTCs as if from measured data sets gathered in occupied homes. The estimated in-use HTCs are compared against SAP-calculated values to illustrate the impact of including or omitting various heat sources and sinks.

The results demonstrate that for dwellings with low heat loss, the increased proportion of heating demand met by unmetered internal and solar gains informs a greater sensitivity of a heat balance estimation of the HTC to their omission. While simple quasi-steady state heat balance methods may be appropriate for dwellings with very high heat loss, alternative approaches are likely to be required for those with lower heat loss.

A need to understand the impacts of unmetered heat flows on the accuracy with which a building’s thermal performance may be inferred from in-use monitored data is identified: this paper illustrates the scale of these impacts for two homes at opposite ends of the energy performance scale.