Chief Statistician’s update: understanding Energy Performance Certificate (EPC) data for Wales

Darllenwch y dudalen hon yn Gymraeg

Today we published an interactive dashboard presenting Energy Performance Certificate (EPC) data for homes in Wales.

Why have we published this dashboard?

Until now there has not been an easily accessible way to look at Wales specific EPC data covering all tenures, which is something users of EPC statistics have told us they would welcome.

What are EPCs?

A valid EPC is required whenever a home is sold or rented. EPCs are valid for 10 years. To obtain an EPC, a qualified energy assessor will inspect a home and record information such as the materials used to build it, the type of building (house, flat, bungalow), the heating system and any insulation to calculate an energy efficiency rating from A (most efficient) to G (least efficient). This rating takes into account the likely energy cost to run the home.

EPC information is lodged on the Energy Performance of Buildings Register held by the Department for Levelling Up, Housing and Communities (DLUHC). Data from the Register can be accessed by anyone via the OpenDataCommunities website.

What is in the dashboard?

In the dashboard we have published today, we have presented breakdowns of the median energy efficiency score and energy efficiency ratings. These measures are the most commonly used to indicate energy efficiency.

We have presented information for valid EPCs (lodged in the past 10 years) only. When looking at the overall picture we have extracted the most recent record for each home.  When looking at specific years, we have extracted the most recent record for each home in that year.

What should be considered when using this dashboard?

The EPC Register is an administrative dataset designed to support government operations (as opposed to statistical and research functions). There are challenges associated with using administrative data for statistics and research, including uncertainty about the quality of data being reported.

One limitation of the EPC dataset is its coverage. Valid EPCs (lodged in the past 10 years) are only available for approximately half of all homes in Wales.

When analysing the EPC data, we have also found a small number of unexpected results. For example, when looking at homes with more than one EPC lodged between January 2013 and December 2022, we found that dwellings rated A in their earliest assessment tended to be rated B, C or D in their more recent assessment. There are a number of possible reasons for this. It could be that changes were made to these homes which caused the energy efficiency to fall, for example adding an extension. It could be that fluctuations in energy prices caused an increase in the estimated energy costs. It could also be that different energy efficiency scores were calculated under different methods (SAP (used for new builds, extensions and changes of use) is produced from a specification while RdSAP (used for existing dwellings) is based on a site assessment). To better understand the data and ensure we use it appropriately, we plan to investigate these findings with colleagues at DLUHC. We also intend to compare results from the Welsh Housing Conditions Survey (WHCS) 2017-18 with EPC records lodged at a similar time. If we find that dwellings received a similar energy efficiency rating in both the EPC and WHCS assessments, we will have more confidence in the quality of the EPC data.

What are the future plans for this dashboard?

The most commonly used measures of energy efficiency have been included in the first version of this dashboard. However, EPCs provide a wealth of other information (such as environmental impact and space heating demand) which, when used alongside the energy efficiency scores and ratings, may provide a more complete picture of energy efficiency. We will explore the value of including other measures in the next iteration of the dashboard in line with users’ priorities.

EPCs also include information about recommended home improvements works which could increase the energy efficiency of a dwelling. We are working with DLUHC to understand how we could best utilise this data. If you have any feedback about the dashboard, or if there is anything you would like to see us include in future iterations, please get in touch with us at

Stephanie Howarth
Chief Statistician