Imagine an apartment that could be teleported across Europe. In Spain, its energy certificate might read D. In Germany, the same apartment could earn a C on a scale that runs to H. In Brussels, it might land on B, one of more than 15 subclasses. In the Netherlands, where the scale climbs to A , it would look positively mediocre.

Same walls, same boiler, same physics, eight different letters.

This is not a thought experiment. It is how Europe has rated its buildings for two decades. Energy performance certificates or EPCs are used across most of Europe. Building energy ratings (BER) are issued in Ireland. In France, Diagnostic de Performance Énergétique (DPE) were introduced under EU law in 2002. Yet each country was left to design its own scale.

The result became known in building-policy circles as the Babel tower of EPCs: dozens of national ladders slicing the same quantity – kilowatt-hours per square metre per year – into incompatible alphabets. Denmark even labels its best homes by vintage, with classes indicating year of construction called A2020, A2015 and A2010.

That tower is now being dismantled. The recast energy performance of buildings directive, in force since May 2024, requires all 27 member states to rebuild their certificates on a single closed scale from A to G. This EU directive had a transposition deadline (the final date by........

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