BRE IP1/15 PDF

Introduction

What is the performance gap?

Buildings rarely perform as well as their designers predicted. Energy consumption can be as much as double what was expected, so annual energy costs can also be doubled. This difference has become known as the ‘performance gap'. In some cases it is due to more intensive or extended occupancy,but often the major cause is that the building services are operated inefficiently and not as intended by the designers.

The performance gap is difficult to quantify because the performance ratings obtained from energy certificates at design and in use are not directly comparable: energy performance certificates (EPCs) measure the theoretical energy performance of buildings, whereas display energy certificates (DECs) measure the buildings' actual energy use. The two ratings measure different things, and each has its value. An EPC is a type of asset rating, whereas a DEC is a type of operational rating. What is missing is a means of relating one to the other[1].