Why DECs are required?

The purpose of introducing Display Energy Certificates is to raise public awareness of energy use and to inform visitors to public buildings about the energy use of a building.

An affected organisation must display a DEC in a prominent place clearly visible to the public and have in its possession or control a valid advisory report. The advisory report contains recommendations for improving the energy performance of the building.

The introduction of DECs will for the first time give publicly accessible information on the energy performance of public buildings. It is important not only that the public sector complies but that it is seen to be setting an example. Environmental performance is increasingly important to reputation. Accordingly if there is any doubt over whether a DEC is required, it would be good practice to produce a DEC in any event.

What is a DEC?

A Display Energy Certificate shows the energy performance of a building based on actual energy consumption as recorded annually over periods up to the last three years (the Operational Rating). The DEC also shows an Asset Rating for this building if this is available (by way of an EPC). A DEC is valid for one year and must be updated annually.

The Operational Rating (OR) is a numerical indicator of the actual annual carbon dioxide emissions from the building. The various types of energy consumption from occupying a building must be brought together on a common basis so that the performance of one building can be compared with that of another. The UK has decided that the common unit should be CO2 emissions, since this is a key driver for energy policy.


This rating is shown on a scale from A to G, where A is the lowest CO2 emissions (best) and G is the highest CO2 emissions (worst). Also shown are the Operational Ratings for the previous two years; this provides information on whether the energy performance of the building is improving or not.

The OR is based on the amount of energy consumed during the occupation of the building over a period of 12 months from meter readings and is compared to a hypothetical building with performance equal to one typical of its type (the benchmark). Typical performance for that type of building would have an OR of 100. A building that resulted in zero CO2 emissions would have an OR of zero, and a building that resulted in twice the typical CO2 emissions would have an OR of 200. If the building is a net energy generator, it would still be given an Operational Rating of zero.

Who needs a DEC?

Display Energy Certificates (DEC’s) are a statutory requirement, since the 1st October 2008, for all public buildings with a total useful floor area exceeding 1,000 sq.m which are regularly frequented by a large number of people and are occupied or part occupied by either:

  • A Public Authority including local and national governments, NHS Trusts, MOD, Schools and Universities, Executive Agencies and Regulatory Bodies
  • A body that provides a public service such as by local or national government to publically display the DEC in a prominent location within the subject building.