A legally required rating (typically A-G) showing how energy-efficient a building is, needed before it can be sold, rented, or in some jurisdictions, occupied. Unlike BREEAM, LEED, or Passivhaus, which are voluntary certifications a client chooses to pursue, an EPC is often a hard legal requirement - and the same energy model or building performance simulation data used to chase a voluntary certification typically produces the EPC rating as a byproduct.