SAP EPCs are known as Standard Assessment Procedure Energy Performance Certificates.
A SAP EPC refers to an Energy Performance Certificate issued from SAP energy calculations by an ‘On Construction Domestic Energy Assessor’ or SAP assessor, using for older non-completed dwellings SAP 2005, SAP 2009 methodology and software - the current version of SAP 2012 is in use for current dwelling designs.
A new dwelling, or dwellings created by conversion/change of use are compulsory to have SAP Calculations carried out. The assessor will then in turn produce an EPC outlining the energy efficiency of that property.
The assessor will use architects plans and drawings, together with detailed information (specifications) around construction, heating and ventilation amongst others.
The two versions of EPC are fundamentally the same thing (the SAP EPC being much more time consuming and needs a very good knowledge of construction), providing a picture of the energy efficiency and energy costs of the dwelling.
Generally, an EPC for an existing dwelling for sale or rental will be much less expensive to purchase than one derived from SAP Calculations.