The government’s consultation on reforming Energy Performance Certificates (EPCs) through the Home Energy Model proposes significant changes to how existing homes are assessed in England and Wales. CIBSE broadly supports the direction, but makes recommendations to improve consumer confidence and delivery against policy objectives.
A key methodological change is the introduction of a modular approach to data inputs. Assessors could rely on default values (as currently in RdSAP) or use more detailed ‘full data’ inputs where reliable evidence exists. CIBSE supports this, as information for existing homes varies significantly. The effectiveness of this approach, however, will depend both on default values and the ‘full’ input alternatives – that is, whether robust measurement methods are widely available.
Further work with industry is required to determine which parameters would be suitable for the ‘full data’ route, through which measurement methods, and under which conditions, including assessor training.
CIBSE also recommends that EPCs include a confidence rating based on the extent of reliance on default vs ‘full data’ inputs. This would help consumers understand the reliability of the EPC and would value more detailed assessments, thereby justifying the additional work, costs and training for assessors.
EPC metrics
The consultation also covers the four new proposed EPC metrics.
The first is fabric energy efficiency (FEE). CIBSE strongly agrees that fabric performance should play a central role, to drive reductions in energy demand and costs, improve thermal comfort, and support decarbonisation. However, it has concerns about the FEE: it is a moving target linked to the notional dwelling and is calculated using standardised assumptions, meaning it cannot be verified in practice. This misses an important opportunity to drive better-quality retrofit works and to monitor outcomes, contradicting the consultation’s aim of encouraging measurement and more reliable data.
There is no explanation for why alternative metrics are not proposed. For example, space heating demand has been recommended by the Climate Change Committee1, and CIBSE is soon to publish a technical memorandum2 on the measurement of Heat Transfer Coefficients (HTCs). The consultation proposes that HTCs could be reported as optional information, but it is unlikely this would happen without incentives.
CIBSE proposes that reporting HTCs or other optional parameters be linked to the confidence rating.
The second metric focuses on heating systems, encouraging efficiency and moving away from fossil fuels. CIBSE broadly agrees with this metric and the proposed rating scale. It recommends that heat networks’ efficiency and carbon content be assessed on the same basis as onsite systems, without accounting approaches such as sleeving and carbon factors for CHP-produced electricity, which artificially reduce the carbon content of network heat.
Furthermore, while acknowledging the potential impact of direct electric systems on the Grid and energy costs, CIBSE notes that they may be viable in very efficient dwellings with extremely low heating demand, with the benefit of being low-embodied carbon. When fully developing the metrics, sensitivity analysis should be carried out on how the stock would fare against the full set of metrics, both currently and in its future intended state – that is, with lower demand and decarbonised.
The most innovative proposal is the Smart Readiness metric, intended to recognise the potential for homes to interact effectively with the energy system. CIBSE supports the intent and broadly agrees with the technologies to be rewarded, but thermal mass should also be recognised as smoothing heat demand. Moreover, given the significant capital costs and resource impacts of batteries, we recommend more analysis on how much and where to reward onsite batteries, with a comparison against Grid-located alternatives.
The consultation does not state what the metric would ultimately measure – whether ratings would simply be based on the list of installed technologies or on a quantitative assessment of outcomes, such as annual energy use or peak demand and potential to shift it , the latter being CIBSE’s recommendation.
The fourth metric covers energy costs. CIBSE supports it as an important parameter for consumers, but little information is given in the consultation. Without careful design and transparent assumptions on tariffs, the rating could be misleading or become obsolete.
About the author
Julie Godefroy is the CIBSE head of net zero
References:
1 Reform of domestic EPC rating metrics to support delivery of net zero, Climate Change Committee, bit.ly/CJEPCCC
2 Plans for guidance on Heat Transfer Coefficients, Julie Godefroy LinkedIn post, bit.ly/4shaX1e