The purpose of introducing Display Energy Certificates (DECs) is to raise public awareness of energy use and to inform visitors to public buildings about the energy use of a building. DECs provide an energy rating of the building from A to G, where A is very efficient and G is the least efficient and are based on the actual amount of metered energy used by the building over a period of 12 months.

Public authorities, and institutions providing public services to a large number of persons, who occupy space in a building with a total useful floor area greater than 1000m2, must display a valid display energy certificate ("DEC") at all times and have a valid advisory report in their possession.

Only public authorities or public institutions (those providing services traditionally associated with local or national government) occupying a building must display a DEC. Other private occupants of the same building are not required to display a DEC.

The DEC is valid for twelve months and is required to be updated annually. The Advisory Report which contains recommendations for improving the energy performance of the building and its energy usage is valid for seven years.

Display Energy Certificates need to be quoted individually for each enquiry. This is due to the differing complexity of the buildings and also the amount of data that needs to be gathered during the site survey.