This guidance will explain the differences between the methodologies and help you decide which is appropriate for an energy assessment on a domestic property.
The SAP methodology is used to assess newly built and newly converted dwellings in order to demonstrate that they comply with the requirements of Building Regulations. In Scotland, a dwelling created by conversion does not require a SAP calculation (such works are exempt from standard 6.1 (carbon dioxide emissions) and standard 6.9 (energy performance certificates).
RdSAP and Newly Completed Domestic Dwellings
RdSAP is for existing dwellings. New dwellings (including conversions from non-domestic or domestic except in Scotland) should have a full SAP assessment when completed and before occupied; however, this is the responsibility of the builder, not the DEA. Having an RdSAP EPC assessment does not preclude a SAP EPC assessment being done later to meet legislative requirements.
Where a property was originally a dwelling but is presently used for other residential purposes and could be reasonably used as a dwelling with no alterations to the building, then an RdSAP EPC can be lodged. Examples would include houses now used as B&Bs or HMOs. Examples that require non-domestic EPCs would be a purpose built hostel or residential home.