The study aims to inform designers about a method for assessing the likely energy consequences of decisions open to them regarding refurbishment options for high-rise housing in the UK. The TAS degrees thermal simulation computer program was used to predict the effects of various improvement measures for a first-floor and a tenth-floor flat. The performances of retrofitted thermal insulation, double glazing, ventilation control measures, and sunspaces were considered. A lifecycle costing method was used to indicate the energy and financial benefits of these improvement options. The results indicated that there was a difference of between 25% and 60% in the predicted heating loads of the first-floor and tenth-floor flats, depending on the improvements installed. Ventilation control measures were found to be the most effective in reducing heating loads and to have progressively greater significance the higher up the building the fat is located. Conversely, wall insulation measures were shown to be the least effective in view of the relatively high percentage of glazing within the external wall areas. The predictions indicated that the provision of sunspaces could not be recommended solely on energy-thrift grounds, because of their high capital costs and low energy savings, but other improvements could be justified over the lifetime simply by taking account of the cost benefit of predicted energy savings. The interaction of the effects of various renovation measures was also considered. Surprisingly, several envelope-insulation measures installed together can save more than the sum of their individual savings, the reasons for this are discussed.