Last edited 20 Oct 2020

National Calculation Method NCM

The National Calculation Method (NCM) is defined by the Department for Communities and Local Government (DCLG). It describes the procedure, for buildings other than dwellings, for demonstrating compliance with the carbon emission requirements of regulation 17C of the Building Regulations and for calculating ‘operational ratings’ and ‘asset ratings’ in the production of Energy Performance Certificates (EPC’s) in relation to the Energy Performance of Buildings Directive (EPBD).

The NCM provides the underlying method and the standard data sets necessary to calculate the annual energy use of a proposed building and comparing it with the energy use of a ‘notional' building of a similar type, under similar circumstances. This is done by calculating the Target Emission Rate (TER - the CO2 emission rate) for the notional building and comparing it with the Building Emission Rate (BER) for the proposed building. The BER must not be higher than the TER.

The calculations can be performed using approved simulation software (Approved Dynamic Simulation Models (DSMs)) or by using the Simplified Building Energy Model (SBEM), a ‘simplified’ compliance tool developed by BRE, which has a user interface called iSBEM.

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