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DECs mean there's no hiding your building's actual energy use

The UK government introduced Display Energy Certificates (DECs) this week for all buildings over 1,000m2 occupied by a public authority. Until now, any new-builds or buildings bought, sold or rented, needed an Energy Performance Certificate (EPC), or asset rating.

While this requires designers to demonstrate an improvement in CO2 emissions against a notional building, the new DEC is based on real meter readings and bills.

The EU came up with DECs to address the fact that public buildings rarely change hands, and occupy a fraction of the new-build sector, so the only way to communicate their efficiency was to report actual energy use. In doing so, it has launched a legislation much more onerous than an EPC – user energy can account for over half of a building’s energy use, and up until now has been unregulated.

This is a momentous change which will bring even the most green boroughs into focus. Increasingly, clients will ask architects and consultants to estimate their future operational ratings. How can architects do this?

Thankfully, organisations such as the Usable Buildings Trust and CIBSE have invested a great deal of time to define CO2 emission benchmarks for key building sectors and benchmark categories, which provide the backbone of the DEC ratings. The CIBSE publication on the revised benchmarks should give a good idea to the more technologically minded architects about the average ratings for a benchmark category. For example, the average annual rating for offices will be somewhere between 70-80kg CO2/m2 but interestingly, the same benchmark will be used regardless of the ventilation system.

CarbonBuzz (, from Chartered Institute of Building Services Engineers (CIBSE) and the RIBA, launches on 5 November. It allows architects and consultants to benchmark their projects against CIBSE’s benchmarks online, anonymously. It provides a visual interface and bridges the gap between forecasted energy use during design, and actual energy use in operation.

Real data would help designers and clients address occupant behaviour, which is a key step towards creating a truly Zero Carbon Britain. Sadly, there are no immediate plans for the government to make the DEC database public, even though architects and engineers need the information to verify whether their ambitious low-energy designs work in practice. So projects like CarbonBuzz, creating an anonymous database of UK projects, will improve the quality and quantity of data available.

While the industry is straining to provide enough inspectors to respond to the urgent need for DEC certificates, the assessment process has created one of the best systems we have for raising awareness of the real energy use of buildings. With organisations such as the British Council for Offices consulting their members on the adoption of voluntary DECs, architects had better take notice.

For more information, visit or go to and search for Display Energy Certificate.

Judit Kimpian is head of sustainability and advanced modelling at Aedas Architects

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