What contributes to the energy performance of a building?

The energy rating of a building is a complex calculation which is based on a combination of factors. The key factors are:

• the type of construction of the building (including walls, roofs, floors and glazing)
• whether parts (zones) of the building are used for different purposes e.g. office, factory etc and the occupancy profile for each zone
• heating, cooling, ventilation and hot water systems used
• lighting

The energy performance of non-dwellings is shown as a CO₂ based index. The CO₂ based rating a building receives depends on the energy used for space heating, water heating, ventilation and lighting, less any energy generated from energy generation technology installed in the building (such as solar water heating). The lower the number the lower the typical CO₂ emissions (based on a scale of zero to 150 +).

The rating is adjusted for the total useful floor area of a building (see glossary of terms for a full definition) so it is independent of size for a given type of building.

The calculation process compares the carbon emissions of the building with those of a reference building. The reference building is an equivalent building (i.e. a building of the same size, shape and use as the actual building) constructed to a notional building designed to a specified standard.