Are Energy Performance Certificates letting heritage homes down?

Posted on: 27 January, 2026

By Associate Professor James Ritson and Professor Graeme Larsen, University of the Built Environment 

Energy Performance Certificates play a central role in the UK’s climate and housing policy. However, growing evidence suggests energy performance certificates (EPCs) are poorly suited to assessing the energy performance of historic homes, with significant implications for owners, policymakers and heritage conservation. 

Energy Performance Certificates (EPCs) are a cornerstone of the UK government’s approach to reducing energy use and carbon emissions from buildings. They influence property transactions, rental eligibility, and long-term targets for improving the environmental performance of the housing stock. 

At the same time, the UK has one of the oldest building stocks in the developed world. It is estimated that up to 80% of the buildings that will exist in 2050 have already been built, and more than 4.7 million homes in England date from before 1919.  

These historic dwellings form a substantial part of the housing landscape and will inevitably play a key role in meeting national climate targets. 

The challenge is that EPCs were not designed with historic buildings in mind.  

Increasingly, research suggests that the way EPCs are calculated can significantly misrepresent the real energy performance of traditionally built homes, leading to inappropriate policy decisions and misguided retrofit interventions. 

How EPCs work and where problems arise 

An EPC provides a rating from A to G based on a modelled estimate of a dwelling’s energy use, fuel costs and carbon emissions. For existing homes, this assessment is usually carried out using a system known as Reduced Data SAP, or RdSAP. 

RdSAP was introduced to make assessments quicker and more affordable by relying on a limited set of inputs and a series of standard assumptions. While this approach works reasonably well for modern buildings with conventional construction methods, it performs far less well when applied to older housing. 

Historic dwellings often use solid walls, breathable materials and construction techniques that vary widely – even within the same period. Over time, they have typically been altered, repaired and adapted in ways that make them highly individual.  

RdSAP, however, relies heavily on assumed characteristics based on age bands, such as wall thickness, floor construction, window proportions and levels of draught-proofing. These assumptions frequently do not reflect the reality of individual buildings. 

As a result, many pre-1919 homes receive low EPC ratings – not because they perform poorly in practice, but because the assessment method is unable to capture their true construction and behaviour. 

The performance gap between prediction and reality 

One of the most significant issues identified in recent studies is the performance gap. This refers to the difference between the energy use predicted by an EPC and the actual energy consumption recorded in use. 

Multiple studies have shown that historic homes often consume substantially less energy than their EPC ratings suggest. Research by English Heritage found actual energy use to be around 40% lower than EPC predictions in traditional dwellings.  

More recent analysis using large datasets of real consumption has shown similar discrepancies, particularly in the EPC bands targeted by government policy. 

This gap has often been attributed to occupant behaviour, based on the assumption that households do not behave like the ‘average home’ used in modelling.  

However, evidence increasingly indicates that the assumptions embedded within RdSAP itself are a major contributor. Default U-values are frequently higher than those measured in situ, leading to systematic overestimation of heat loss.  

In simple terms, many historic walls are assumed to perform worse than they actually do. 

Why effective improvements are undervalued 

There is a further problem with how EPCs influence decisions about building improvements. Conservation and heritage bodies have long advocated a whole-house approach for historic dwellings, prioritising maintenance and low-impact measures that improve performance without damaging historic fabric. 

Such measures include improved loft insulation, draught-proofing, efficient boilers, enhanced heating controls, secondary glazing and regular maintenance of windows, roofs and rainwater goods.  

Research shows that these benign or shallow retrofit interventions can reduce energy use and carbon emissions by 30%-50% in pre-1919 homes. 

Despite their effectiveness, many of these measures have little impact on EPC scores because RdSAP places greater emphasis on fuel type and assumed fabric performance. 

As a result, EPC recommendations often favour more invasive and costly interventions, such as internal or external wall insulation, which may be technically inappropriate for breathable historic structures and potentially harmful to their long-term condition. 

Case studies demonstrate that equivalent improvements in energy performance can often be achieved at a fraction of the cost suggested by EPC reports when more detailed and flexible assessment tools are used. 

The overlooked importance of maintenance 

A critical omission in the current EPC framework is the condition of the building. For historic dwellings, maintenance plays a central role in energy performance. Poorly maintained buildings are more likely to suffer from heat loss, damp and inefficient systems, while well-maintained buildings often perform far better than predicted. 

Despite this, the EPC includes no assessment of a dwelling’s state of repair. This omission is widely recognised by conservation organisations, which emphasise that regular maintenance is one of the most cost-effective and energy-efficient interventions available.  

Implications for policy and practice 

EPC ratings are increasingly tied to regulation. Landlords are already prohibited from letting properties below EPC band E, and current policy aims for all homes to reach band C by 2035. If EPCs systematically underestimate the performance of historic dwellings, these policies risk placing disproportionate pressure on owners of older homes and encouraging inappropriate interventions. 

This is not an argument against improving the environmental performance of historic housing. Rather, it is a call for assessment methods that are accurate, proportionate and appropriate to the buildings being evaluated. 

EPCs must evolve 

If the UK is to meet its sustainability targets while protecting its historic housing stock, the EPC framework must evolve.  

This includes accounting for building condition, incorporating actual energy consumption data where possible, and allowing more nuanced assessment methods for traditionally built homes.  

Without such changes, EPCs will continue to misrepresent the performance of historic dwellings and undermine both environmental objectives and heritage conservation.

Associate Professor James Ritson is the Programme leader for MSc Innovation in Sustainable Built Environments

Professor Graeme Larsen is the Associate Dean of Sustainability at the University of the Built Environment