In accordance with commitments under the national climate change strategy, part L of the national building regulations and the related technical guidance document L – Conservation of Fuel and Energy – has been amended for new dwellings with effect from 1 January 2003. The normal window performance expected has been considerably improved with double glazing incorporating low-e glass now being the norm. This represents a reduction in heat loss through glazing of some 33% compared to standard double-glazing. These requirements in relation to glazing will also apply to replacement windows – in the context of alterations of existing houses – with effect from 1 July 2003. These upgraded requirements for windows in dwellings are in line with advanced energy conservation requirements in other European countries.