In June of 2003 a revised Part L of the Building Regulations Approved Documents increased the stringency of requirements pertaining to the conservation of fuel and power in buildings. These regulations are indicative of the increasing pressure that is being applied to legislators, architects and builders to improve the energy efficiency of the British construction industry. In particular, the new Part L1 significantly increases the demands placed on housing. Furthermore, these regulations no longer apply purely to new build dwellings, but to any building work that is deemed to constitute 'material alterations'. While the government's commitment to driving forward standards of 'good' new housing is clear, the extent to which the existing, and increasingly elderly, housing stock can be improved is less certain. This study investigates the potential for increasing the energy efficiency of existing dwellings, up to and beyond current standards. A survey of ten percent of the dwellings in Neath Port Talbot County Borough is used to analyse predominant physical characteristics of housing. The houses are clustered into twenty groups based on these characteristics.A n actual dwelling is then chosen that is most representative of each of the groups, and is surveyed in detail. Dynamic computer models of these dwellings are used to evaluate the impact of a series of different energy efficiency measures, ranging from simple home improvements to more complex refurbishments. Returning to the larger scale, conclusions are drawn relating to the degree that the energy efficiency of existing housing stock can, and should, be improved. The efficiency of the houses as existing is significantly influenced by dwelling type, age, occupancy and the degree of care that has been provided by owners and occupiers in maintaining their homes. However, some of the emergent dwelling types have more efficient physical forms than others. Improvement of glazing has the biggest impact on the energy consumption of most of the dwellings, typically reducing fuel bills by a third, although it is not likely to be the most cost effective measure. When coupled with replacement of the boiler, saving on average 17.5% of the heating load, this unanimously results in a very significant saving. Improvement of the dwellings generally to current standards typically reduces the energy required for space heating to one third of current heating loads. Terraces and flats provide very efficient forms for improvement. The smaller semi detached houses perform acceptably at higher standards, whereas larger semi- and detached homes and particularly bungalows are intrinsically less efficient. Orientation plays an important part in achieving higher standards. Large, recently built houses tend to have a uniformity of windows that lose energy, while older houses are very often more thoughtfully and responsively designed. Improvement of the dwellings to super-insulated standards reduces the overall energy required for space heating to only a seventh of the current demand. Only the smallest, most sheltered homes with good orientation can achieve autonomous standards, and this requires air-tight fabric and energy from renewable sources.