EPC ratings shown to be 'staggeringly inaccurate' by report

Insulating a loft
EPCs take into account a building's insulation (Image credit: Getty Images)

Energy certificates are “staggeringly inaccurate” and energy efficiency upgrades make little difference to the climate crisis or energy bills, an investigation by The Sunday Times claims.

An Energy Performance Certificate (EPC) is a document that sets out the assessed energy efficiency and potential CO2 emissions for a property. The property is rated on a scale from A to G with A being excellent and G a disaster.

Very, very few houses achieve an A-rating and most tend to be D or above. They are required whether you're building, buying, selling or renting a house.

The newspaper, which called the findings a "national scandal", uses research from CarbonLaces, which found EPCs overestimate energy use by up to 344%. Meanwhile, other energy and sustainability experts have expressed concern about the accuracy of the research

What were CarbonLaces findings?

The Times story states that CarbonLaces compared the EPCs of more than 17,000 homes with their actual use, as logged by smart meters every half hour for at least 300 days.

The average metered gas and electricity use for all the properties studied was 125kWh per square metre a year, a total of 91% lower than what their EPCs claim.

CarbonLaces founder Madhuban Kumar said: “The inaccuracy increases exponentially for energy-inefficient homes. It shows the government may be over-allocating taxpayers’ money to upgrade homes with the worst ratings.”

The report adds that D-rated homes, the most common grade across Britain, have a 52% overestimation and the reality gap is 161% for homes rated F, 90 per cent for E and 23% for C. The most accurate EPC ratings are A and B, although they still slightly underestimate the actual energy use. You can find out more on what is your home's energy rating in our guide.

What has the reaction been to this report?

Environmental writer Kate de Selincourt tweeted that The Sunday Times article seems to fundamentally misrepresent what EPCs are intended for.

She wrote: “They aren't meant to predict individual household energy use - they just compare and rank how different buildings would serve that same household.

“I'm concerned that the burden of the article seems to edge in the direction of ‘EPCs are all lies so landlords are being made to upgrade properties that are already perfectly good’. That really isn't what we should be taking away from this."

Why has the report been met with mixed reactions?

Andrew Sissons, of social innovation agency Nesta, said the article was “interesting” and admits EPCs have many flaws and need to be improved.

However, he wrote on social media: “EPCs are not meant to measure actual energy use, but how efficiently a home uses energy. These aren’t the same thing. Many inefficient homes, for example, are under-heated because their occupants can’t afford enough energy."

But building physicist Dr Sarah Price disagreed, saying: “Finally, the research to back up something I've suspected for a long time. EPCs are not worth the paper they are written on.”

A blog entry from Elmshurst Energy strongly advises caution over simply stating that EPCs are misleading. It says: “It is vital to understand that an energy assessment and the EPC is based on standard occupancy e.g. a family living in the property operating the home on set temperatures and running times.

“The EPC predicts the heating, hot water and lighting for the home based on average use patterns and average weather conditions. They continue to serve their original purpose by enabling homebuyers or renters to compare the energy efficiency of properties and make informed decisions.”

Managing director Stuart Fairlie said: “Apples and Pears spring to mind here, as Elmhurst have advocated for many years that the EPC must give equal prominence to cost, carbon and consumption.

“EPCs are currently limited to a cost metric, but are still used as a policy tool to reduce carbon emissions from housing and to tackle climate change.”

How useful is an EPC?

Our own energy expert Tim Pullen explains what is an EPC in more detail in his expert guide, and wrote about the concerns some have expressed about EPCs.

He notes that some of the improvements suggested by the software used to generate EPCs are ridiculous. He cites the example of recommending the installation of cavity wall insulation to the owner of a 19th century house, with 500mm thick solid stone walls. The result was that the whole document was dismissed as being a farce.  

He said: “We can conclude therefore, that if the reader is prepared to believe it, the EPC will have value. But that the methodology currently used to produce them does not instil any confidence in their accuracy or efficacy.”

Sam Webb

Sam is based in Coventry and has been a news reporter for nearly 20 years. His work has featured in the Mirror, The Sun, MailOnline, the Independent, and news outlets throughout the world.  As a copywriter, he has written for clients as diverse as Saint-Gobain, Michelin, Halfords Autocentre, Great British Heating, and Irwin Industrial Tools. During the pandemic, he converted a van into a mini-camper and is currently planning to convert his shed into an office and Star Wars shrine.