DECs provide an energy rating of the building from A to G, where A is very efficient and G is the least efficient and they are based on the actual amount of metered energy used by the building over a period of 12 months. They also show ratings for the previous two years for comparison.

A DEC must be provided for a building (or part of a building which is designed or altered to be used separately) with a total useable floor area of over 250 m2 (total useable floor area is defined as the total area of all enclosed spaces measured to the internal face of the external walls, including areas such as staircases and galleries) which is occupied by a public authority.

The DEC must be accompanied by an Recommendation Report containing cost-effective recommendations for improving the energy efficiency of the building. It should enable the occupier to identify what may be done to improve energy management and reduce energy consumption and CO2 emissions.

A local authority can issue a penalty charge notice of £500 for failing to display a DEC at all times in a prominent place clearly visible to the public, and £1,000 for failing to possess or have in their control a valid Recommendation Report. In addition to these penalties, it will still be necessary to commission the documents, otherwise further offences will be committed.