From 9 January 2013, A DEC and advisory report are required for buildings that are occupied in whole or part by
public authorities and frequently visited by the public, and has a total useful floor area over 500m². DEC and advisory report for buildings between 500 m² and 1000m² are valid for 10 years, whilst the DEC for buildings over 1000m² remain valid for 1 year and advisory report 7 years. If you are a new occupier, or have been in occupation for less than 15 months by 9 January 2013, you may not have the previous 12 months of meter readings available that are required for an operational rating. The legislation makes provisions for calculation over the period of occupation in these cases.
The purpose of introducing 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 the last 12 months within the validity period of the DEC.
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.