We explain the numbers found on the SAP Assessment.
The Government Standard Assessment Procedure or (SAP for short) is used as the methodology within England and Wales to assess the energy performance of domestic dwellings. This assessment has been introduced to meet the requirements set out by the European Energy Performance of Buildings Directive. To help show the energy performance of the dwelling several key energy indicators have been devised. These are energy consumption per unit floor area; an energy cost rating (the SAP Rating); an Environmental Impact Rating based on the CO2 emissions of the dwelling. (also known as the EI Rating); and lastly a Dwelling CO2 Emission Rating or DER. The Energy Cost Rating (SAP Rating) is based on the cost associated with energy consumption within the dwelling, taking into account things like Space Heating, Water Heating and Lighting. Counter measures can be used to reduce the Energy Cost of the dwelling, e.g. energy generating technologies such as Photovoltaic Panels (PV). To be able to compare different dwellings like for like, it is necessary to then adjust this value using the Floor Area, thus giving a value that is independent from the size of the dwelling. The SAP Rating is expressed on a scale of 1 to 100, with the higher number indicating a dwelling with lower energy running costs. In contrast the Energy Impact Rating (EI Rating) measures the actual CO2 emissions produced as a result of energy used within the dwelling, instead of the associated financial cost. Like the SAP Rating, it takes into account any reductions in emissions gained from using new energy generating technologies and, again, is adjusted for floor area to enable comparisons to be made between dwellings. The EI Rating is expressed on a scale from 1 to 100: those dwellings achieving a higher score are those with reduced CO2 emissions. The Dwelling CO2 Emission Rate (DER) is used to show Building Regulation compliance, and, like the Energy Impact Rating above, measures the amount of CO2 emitted from the dwelling. However, instead of providing the information on a scale, the actual annual CO2 emissions per unit floor area expressed in kg/m2 per year is used. As per the other ratings the DER takes into account the CO2 emissions associated with space and water heating, ventilation and lighting, less any energy generated from energy generation technologies.