When a building is refurbished, energy conservation measures might be profitable to implement. The profitability depends, among other things, on the electricity and district-heating tariffs, the unit price for oil, etc. The cost for the retrofit is of course also important as well as the influence of the retrofit on the demand for heat in the building. By the use of a Mixed integer Linear Programming model of a building, a number of different optimal retrofit strategies are found depending on the energy cost. The result shows that the Life-Cycle Cost for the building is subject only to small changes as long as the optimal strategies are chosen. Most important is the heating system, while building retrofits such as added insulation, are too expensive to take part in the optimal solution.