The survey needed to produce an EPC is performed by an assessor who visits the property, examines key items such as build form, insulation levels in walls, floor & loft, domestic heating system, hot water tank, radiators, windows, lighting and any renewables used within the property . The information gathered is entered into a RDSAP software program derived from the UK Building Research Establishment's Domestic Energy Model (BREDEM), which performs the calculation of energy efficiency. The program gives a single number for the rating of energy efficiency, and a recommended value of the potential for improvement. There are similar figures for environmental impact. A table of estimated energy bills per annum (and the potential for improvement) is also presented, but without any reference to householder bills. The exercise is entirely non-invasive, so assessors make assumptions on the insulation properties of various elements of the property based on age and construction type. The assessor has the ability to over-ride these assumptions if visual or written evidence is provided to support the presence of insulation which may have been subsequently installed. EPCs have to be produced by domestic energy assessors who are registered under an approved certification scheme.
The A to G Scale
Energy Performance Certificates present the energy efficiency of dwellings on a scale of A to G. The most efficient homes – which should have the lowest fuel bills – are in band A. The certificate uses the same scale to define the impact a home has on the environment. Better-rated homes should have less impact through carbon dioxide (CO2) emissions. The average property in the UK is in band D or E for both ratings.