An Energy Performance Certificate (EPC) is now required whenever a building is built, sold or rented. The certificate provides 'A' to 'G' ratings for the building, with 'A' being the most energy efficient. The current average rating is 'D'.

This is part of the Energy Performance of Buildings Directive, which all EU member states must adopt.
EPCs come with information on a building's energy use and carbon dioxide emissions and a report with recommendations to reduce energy use and carbon dioxide emissions.
Interseasonal Heat Transfer™ is ideally suited to well insulated new buildings.
Please see: What IHT is.
See also: Retrofitting IHT to save carbon emissions.