The government's much trumpeted "green deal" has shifted the energy efficiency of our homes further up the political agenda. Rightly so, given they are responsible for more than one-quarter of the UK's carbon emissions.

But our 2m non-residential buildings are energy guzzlers as well, responsible for an additional 17% of UK emissions. In this sector we have a two-tier system, where every public building is required to have an A-G rating of its carbon performance displayed prominently in its foyer – but where commercial buildings don't. That's got to change.

The A-G rating, called the Display Energy Certificate (DEC), has an accompanying report advising on how to improve performance. That might mean improving heating and cooling systems, better insulation and low-energy lighting – all of which, of course, saves money.

Chris Huhne, the climate and energy secretary, shouldn't need much persuading of how useful DECs can be, given his department's HQ has gone from a G rating in 2008 to an E rating today. An E may not sound brilliant, but it's a significant improvement. After a fit-out, they are well on the way to electricity consumption being cut by one-fifth and gas use by a two-thirds. Even more impressive, this has happened while occupancy has doubled.

Getting an A-G rating is all about getting good data. As the old saying goes: "if you can't measure it, you can't manage it". That phrase rings particularly true in the case of one public building (that shall remain nameless), where the process of producing the DEC uncovered the fact that the building had a faulty electricity meter. Remarkably, they (or we, the taxpayer) had overpaid for its power by nearly £400,000 over a five-year period. That cash is now in the process of being recouped from the energy companies involved.

So what's preventing us in the commercial sector producing its own DECs? Unfortunately, but understandably, businesses are waiting for each other to make the first move. Why take the flak given many will be at the lower end of the scale?

It may sound like turkeys voting for Christmas, but commercial building owners have been crying out for DECs to be rolled out. As long as it's an even playing field, the view is that robust DECs will enable investors to assess property portfolios on their energy performance, and that over time, lower ratings will be seen as obsolete stock that needs to be improved.

It would also help to make or break a business's reputation among consumers, who would be able to see A-G ratings displayed in their local shops, bank or even pub. With so many big companies talking a very good game on sustainability, this is an opportunity to sort the green from the greenwash.