New Build versus Existing Properties

For domestic properties, ie houses and homes rather than commercial premises, there are two different assessment procedures used in the creation of EPCs.

For new-build properties, an EPC is generated using the Standard Assessment Procudure, known colloquially as SAP. This is based on engineering information about the materials used in the construction of the property, and is created by an On Construction Domestic Energy Assessor (OCDEA), without a visit being required by them to the property.

For existing properties however, i.e. properties that are more than 10 years old and where the original SAP EPC has now expired, a new EPC is generated using the Reduced Dataset Standard Assessment Procedure, known as RDSAP. This requires a visit from a Domestic Energy Assessor (DEA), and makes use of less detailed information, and assumptions are made behind the scenes about various aspects of the property.

It is worth mentioning that it's quite possible that if you have a house that is now just over 10 years old, and you decide to get a new EPC generated in order to sell that property, that the rating on this new EPC may be lower than that on the original SAP EPC.

The type of assessment procedure used for creating an EPC is specified on the certificate itself. By looking closely at an EPC, you will be able to determine which procedure was used.