An estimated 15% of energy performance certificate (EPC) ratings of residential properties are wrong, according to new research.
An estimated 35,028 E-rated properties are being let illegally, having borderline EPC scores that would likely be downgraded to F if their area was accurately measured, the authors claims.
Errors are caused by inaccurate measurements of properties, particularly where rooms are irregularly shaped.
The study, Impacts of inaccurate area measurement on EPC rating, was conducted by Nirushika Nagarajah of the University of London and Joseph James Davis of the University of Kent.
They found that 90% of EPCs lodged use the reduced data standard assessment procedure, which employs standardised values, rather than actual measurement of many features.
Limited measurement practices and standards, combined with the use of average storey heights mean wide margins of error on the primary dwelling volume input factor.
Modern measurement tools and accurate consideration of the actual volumetric space to be heated vs heat loss areas would radically improve the accuracy of EPC assessment procedures, they say.
The report was published by Spec, which produces high-tech 3D measuring kit. The full report can be found at spec.co