SAP, also known as standard assessment procedure, is a UK normalisation method to measure energy efficiency within a building, with this also being used for renewable technologies. Sap is in the Part L of the building regulations of 1994, which are states for building performance.  

 A SAP is completed by assessing the amount of energy that a building will use while still providing comfort and service. This assessment is done upon standardise assumptions of the occupancy. This will allow for a like-for-like analysing of building performance. This would imply fuel cost and emission of carbon dioxide CO2, this would be determined for the assessment. SAP is the performance of a building, which would include energy use per unit floor area, fuel cost-based energy efficiency rating, this would be the SAP rating and emissions of CO2. These performances are completed on estimates of annual energy consumption based on the establishment of domestic hot water, heating, lighting and ventilation. SAP outputs would contain energy usage of appliances, potential overheating in summer, and the subsequent of cooling loads.  

Basic overview of the differences between SAP and EPC 

This is not a site visit or survey that is needed, as the assessor will only need the required information for the assessment. The SAP that you’ll be providing is the methodology behind all the important information that is processed into an EPC, and it is a list of calculations that justify the entire performance of a building. The EPC is just the identification of those calculations.