The BRE Trust has carried out a unique data analysis project which interrogated the Display Energy Certificate (DEC) statistics of more than 28,000 public sector buildings.

Results show that while DECs are valuable they do not provide evidence of real energy efficiency improvements and carbon emission reductions in public sector buildings.

The DEC is a record of the building's metered energy usage and associated carbon emissions over a 12-month period, and compares these against established benchmarks to give a rating from A (best) to G (poorest).

Jon Mussett, Principal Sustainability Consultant at BRE said: "Energy used in public buildings accounts for 4% of the UK's carbon emissions. Design standards are improving, but we need to demonstrate that this is resulting in improved building performance.

"The study found that the DEC ratings for some schools recently refurbished to higher energy efficiency standards under Building Schools for the Future and the Primary Capital Programme appeared to be no better than average. If expected savings are not being made, we need to learn the reasons why. DECs are important because they measure the carbon emissions from real buildings as they are used."

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It has been suggested that DECs should be made mandatory for all non-domestic buildings, to provide evidence of actual emissions and potential leverage for improvements.

The BRE study found that the benchmarks were appropriate and that DECs were generally giving consistent results. However, up to 9% of DEC data is unreliable as a guide to the energy and carbon performance of buildings because default ratings are being used. This is most common for job centres (17%) and academies (23%). A further 2% of DECs were found to have values which are questionable in some way, for example, 37% of A rated buildings, the most energy efficient category, are listed in the database with a zero rating.

Jon Mussett added: "DECs are a potentially powerful source of information about the carbon performance of the public sector estate, but the results are hard to access and difficult to correlate with other datasets in order to draw meaningful conclusions to inform departmental carbon reduction strategies.

"Thousands of buildings are now producing DECs for the second year - the Government should seize this opportunity to detect and measure trends in carbon emissions in different parts of the public estate to help inform future policy."

(CD/GK)