What's an EPC?

A domestic Energy Performance Certificate (EPC) is a mandatory document which house sellers must commission before they can advertise their property for sale, and which must be received and paid for no later than 28 days after this point in time. EPCs are generated as a result of input collected by a trained and accredited Domestic Energy Assessor (DEA) while carrying out a thorough visual inspection of a property.

The certificate contains three main elements:

the Energy Efficiency Rating. This is a measure of the overall efficiency of a home in terms of cost of fuel consumption per square meter of floor area. When comparing EPC data for different properties it is important to keep in mind that fuel prices may have changed since the certificate was issued - hence the reliability of EPCs falls rapidly in times of large fuel price changes.
the Environmental Impact Rating, a measure of how much CO₂ the home emits; and
a list of suggested improvements if relevant to the property.

The accuracy of the method used to calculate these values, Reduced Data Standard Assessment Procedure (RdSAP), is quite low. It is based on a large number of assumptions, 'typical' values and estimates, and it is perhaps fair to claim that the political factors carry as much weight as the scientific factors in this whole procedure.

Based on the DEA's measurements, the date of the property and the dates and properties of any extensions and improvements, RdSAP calculates two sets of figures for Energy use (in kWH/m²a), CO₂ emissions (in ta^-1) and fuel costs (in £a^-1), a set illustrating the current standard of the property, and a set illustrating the potential standard attainable if the suggested improvements are implemented.

The numbers are normalised onto a non-linear scale yielding ratings in bands, from G to A, where A is the best rating, i.e. the lowest consumption and emission (see the figure).

Furthermore, the performance is broken down by elements such as walls, roof, main heating, etc, so you can see the prevalent causes of a given rating. This is done on a five-point scale ranging from "very poor" to "very good".

With regard to the suggestions for improvements these are split into three groups, lower cost measures, higher cost measures, and further measures. The lower cost measures generally cost up to around £500 to implement, and some of them may be carried out on a DIY basis. (We would tend not to recommend this except in the simplest cases because we see so many cases of incorrectly installed insulation materials, etc, leading to damage from damp). Higher cost and further measures will almost always require professional installation.

Your friendly DEA will be able to explain the contents of the EPC whereas advising you with regard to the individual measures lies outside his remit.

Other types of EPCs include Display Energy Performance Certificates and Commercial Energy Performance Certificates.