A common misunderstanding with building design is that all energy loads are accounted for in the calculations undertaken in the Building Regulations Part L Conservation of Fuel and Power compliance checks. This is not the case. The Part L [SBEM] calculations only determine the CO₂ emissions for a building's regulated [energy] load according to set conditions.

The regulated carbon emissions for gas and electricity include emissions from heating, cooling, hot water, auxiliary equipment (fans, pumps and controls) and lighting. All other equipment 'plugged' into the buildings gas and electric network (computers, catering, process loads, lifts, etc.) are deemed as non-regulated loads and excluded from the Part L assessment.

For the purposes of Part L, the [SBEM] assessment only covers the energy efficiency of the building as a 'shell' which ensures the fabric attains minimum thermal performance standards and the fixed building services achieve minimum system efficiencies. Therefore, the BRUKL output report produced from the SBEM can never be used to forecast the operational energy consumption of a property.