An Energy Performance Certificate will show the official energy efficiency rating of a property.

The certificate provides a rating for the building, (similar to the rating certificates now provided with domestic appliances such as refrigerators and washing machines). Showing its energy efficiency and its environmental impact on a scale from A-G (where A is the most efficient and G the least efficient). It will also contain recommended ways to improve the building's energy performance.

Two ratings are shown. The environmental impact rating (right top) is a measure of a home's impact on the environment in terms of carbon dioxide (C02) emissions the higher the rating, the less impact it has on the environment. The energy efficiency rating (right bottom) is a measure of a home's overall efficiency. The higher the rating, the more energy-efficient the home is, and the lower the fuel bills are likely to be.

Each rating is based on the performance of the building itself and its services (such as heating and lighting), rather than the domestic appliances within it. This is known as an asset rating. The certificate will also list the potential rating of the building if all the cost-effective measures were installed.

The ratings will vary according to the age, location, size and condition of the building. The potential rating on the certificate will take these factors into account, and the suggested measures will be tailored so that they are realistic for the particular building.

By 2009, all buildings in the UK which are constructed, sold or rented out will have to have an Energy Performance Certificate, in accordance with the European Energy Performance of Buildings Directive.

Predicted and interim energy assessments are for homes that are not yet built. When a home is designed, a predicted energy rating based on the design is produced. This must achieve, as a minimum, the target energy rating laid down for the home as specified by the energy efficiency requirements of building regulations.

Interim energy assessments are for new homes built in accordance with the energy efficiency requirements of the building regulations that came into force in April 2006. For these homes, only the energy-efficiency and environmental-impact graphs will be required, and not the full Energy Performance Certificate.