What is an Energy Performance Certificate?
An Energy Performance Certificate (EPC) is a report and energy efficiency rating issued to a property after an energy assessment survey has been carried out. An energy rating must be determined whenever a house is built, sold, rented or has grants applied for under the Energy Company Obligation (ECO) scheme.
An EPC report assigns an energy efficiency rating from A (most efficient) to G (least efficient) based on the energy performance of a property. An EPC is generally required by any property that hasn't had one in the last 10 years and is not exempt based on listed building status.
How accurate are EPCs ratings?
EPCs are a fairly blunt instrument for rating a property based on its age, built form, construction, heating system and level of insulation. They use this information to build a simple energy model using the Reduced data Standard Assessment Procedure (RdSAP) method.
The floor plan, boiler efficiency and other information collected by an EPC assessor are all subject to human error. If an energy assessor has miscalculated the floor area or input any information incorrectly, it is possible that an inaccurate EPC rating will be produced.
Research has shown that using outdated techniques to measure dimensions of buildings has had a significant impact on the accuracy of EPCs. One in four EPCs has been shown to record the floor area of a property so inaccurately that it varied by more than 10% from the true size.
Inaccurate floor areas will have an impact on the calculated heat loss and air permeability of buildings. An EPC rating should therefore only be considered a rough estimate of a property's energy efficiency and can never measure its true in-situ performance, which will vary between buildings of the same design and likely deteriorate over its lifespan.
Build Test Solutions portfolio of unique building diagnostic and measurement solutions are designed to accurately measure the true performance of buildings and make energy efficiency ratings more accurate.
New EPC assessments allow you to input a measured airtightness value and measured U-values into the RdSAP software. Airtightness can be measured using a Pulse air permeability system, whilst in-situ U-values can be determined using Heat3D infrared thermography or heat flux plates. Providing evidence of measured values such as these can lead to a lower rating and EPC band.