A key requirement for new dwellings is a minimum overall energy performance standard, in terms of a Target carbon dioxide Emission Rate (TER). Calculating a Dwelling carbon dioxide Emission Rate (DER) for the actual dwelling and ensuring that this is no greater than the TER will be part of the overall requirement to demonstrate compliance.
 
A further key requirement will be for the performance of the building fabric and the fixed building services to be no worse than specific design limits set out in the approved document. The aim is to reduce heating demand by limiting heat loss through the fabric of the dwelling and place limits on design flexibility to discourage excessive and inappropriate trade-off (for example dwellings with poor insulation levels made to comply by using renewable energy systems).

The full set of criterion which will need to be demonstrated in order to comply can be seen in the interim version of AD L1A.

The changes to AD L1B recognise the increasing importance of existing stock, and have extended the range of energy efficiency improvements which should be carried out at the appropriate opportunity. Requirements now cover aspects such as worst acceptable U-values for walls, roofs and floors when replacing elements in an existing dwelling and also cover areas such internal lighting.

In keeping with the European Union's Energy Performance of Buildings Directive (EPBD) and our own Government's Energy White Paper further amendments of Part L are likely in 2010 and 2015.