A Display Energy Certificate is a certificate shwoing the operational energy performance of s building based on actual energy consumption as recorded annually over priods up to the last three years. DECs need to be updated each year.

What buildings are affected?

• Only buildings occupied or part occupied either by a public authority or an institution, that provides a public service, and expect to be visited by the public to a large number of persons and who are therefore frequently visited by those persons, and
  
  
• have a total useful floor area greater than 1000 metres squared.

Where a building is partly occupied by a public authority or a relevant institution, the authority or institution is responsible for displaying a DEC and having a valid advisory report. Other private organisations occupying the building, irrespective of the size they occupy, do not need to display a DEC.

What is the difference between DECs and EPCs?

• An EPC is required when a building is constructed, sold or let and is renewable every 10 years. An EPC shows the Asset Rating for a building that is the protential energy performance that each specific building can achieve, whereas DECs are only assessed compared to 'the avergae energy performance for a building of this type' which is set at 100. A building may reuire both and there is an opportunity to put the Asset Rating on the DEC.
  
  
• The benchmark of 100 is based upon a Chartered Institute of Building Services Engineers (CIBSE) report which includes 29 categories of building.