Current office buildings are becoming more and more energy efficient. In particular the importance of heating is decreasing, but the share of electricity use is increasing. When the CO
2 equivalent emissions are considered, the CO
2 emissions from embodied energy make up
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Current office buildings are becoming more and more energy efficient. In particular the importance of heating is decreasing, but the share of electricity use is increasing. When the CO
2 equivalent emissions are considered, the CO
2 emissions from embodied energy make up an important share of the total, indicating that the building materials have a high importance which is often ignored when only the energy efficiency of running the building is considered. This paper studies a new office building in design phase and offers different alternatives to influence building energy consumption, CO
2 equivalent emissions from embodied energy from building materials and CO
2 equivalent emissions from energy use and how their relationships should be treated. In addition this paper studies how we should weight the primary energy use and the CO
2 equivalent emissions of different design options. The results showed that the reduction of energy use reduces both the primary energy use and CO
2 equivalent emissions. Especially the reduction of electricity use has a high importance for both primary energy use and CO
2 emissions when fossil fuels are used. The lowest CO
2 equivalent emissions were achieved when bio-based, renewable energies or nuclear power was used to supply energy for the office building. Evidently then the share of CO
2 equivalent emissions from the embodied energy of building materials and products became the dominant source of CO
2 equivalent emissions. The lowest primary energy was achieved when bio-based local heating or renewable energies, in addition to district cooling, were used. The highest primary energy was for the nuclear power option.
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