In Sweden, the activity on building new residences has been decreased for a number of years. The building stock as an average has therefore become older and in the future it will be subject for refurbishment. This paper deals with how to optimise retrofit measures, i.e. how to act in order to minimise the Life-Cycle Cost (LCC) of a building. Insulation measures are emphasised but also other retrofits are dealt with such as changing the heating system. It is shown that the heating system has a vital influence on the optimal amount of extra insulation which is to be applied. District heating is common in Sweden at least for larger buildings such as multi-family block of flats sited in urban areas. The tariffs for district heat must therefore be properly addressed in order to find out if extra insulation is profitable or not. As an example the Navestad area in Norrkoping is used. This residential area is now the subject for extensive retrofitting.