The energy saving potential of existing buildings is significant compared to new buildings in the EU region. To reduce significantly the CO2 emissions of buildings, energy efficiency of old buildings need to be improved. Aim of this study is to determine cost-optimal solutions for energy renovation and renewable energy production systems for an old existing service building. The example building of this study is a residence for elderly people, which was built in 1955 and located in Finland. This study was carried out by a dynamic building simulation tool IDA-ICE and multi objective optimization tool MOBO. The cost-optimal renovation concepts were determined from over 2.6 billion renovation measure combinations to minimize both target energy consumption and life-cycle costs over 20 years. The results show that air-to-water heat pump is more cost effective heating system for the studied building than district heating from the building owner point of view. Improving thermal insulation level of the external walls from the original level is not the most cost-effective option to improve the energy efficiency of the building. Instead of that, for example, installation of PV and solar thermal systems are recommended in all the cost-optimal solutions regardless of the target energy consumption level.