To comply with Part L1A (new dwellings), a 'Design Stage' calculation must be submitted to Building Control prior to commencement of works to show that the Dwelling Emission Rate (DER) from the proposed dwelling is no greater than a Target Emission Rate (TER). In England the dwelling must also achieve a Fabric Energy Efficiency Standard (FEES), however in Wales minimum mandatory U-Values must be met. An additional calculation carried out on completion ensures that the Final 'As-Built' project still meets the requirements.
To comply with Part L1B (extensions to existing dwellings/change of use) for small works, compliance can be gained by achieving set elemental U-values for the floors, walls and roofs. More commonly, and in order to give designers increased flexibility, a comparative carbon emission (SAP) calculation can be used to demonstrate a reduction in overall carbon emissions. This is often achieved by off-setting or upgrading selected areas of the 'existing dwelling'.
To comply with Part L2A (work in new non-domestic buildings), the overall CO2 emissions, or Building Emission Rate (BER), from the proposed building should be no greater than a predetermined Target Emission Rate (TER) which is derived from an energy calculation called the Simplified Building Energy Model (SBEM).
To comply with Part L2B (work in existing buildings that are not dwellings), there is a need for ‘consequential improvement’. Where work involves an extension or the installation of fixed building services (or an increase in capacity of these building services), there is a need to improve the overall energy performance of the building.