This paper presents a case study of a single-family house, where the effect of using thermal energy storage integrated in the floor is evaluated regarding GHG-emissions during the life cycle. The house has a lightweight wood frame construction, is well insulated, and fulfils the Norwegian energy regulations from 2010. Different floor configurations have been studied, both regarding energy demand and emissions. Floors with PCM panels have been compared with a reference case without thermal energy storage integrated in the floor, and have also been compared with concrete and wood as replacement for the PCM panels. The effect of changing the thickness of the PCM, concrete and wood has also been investigated (5 mm, 25 mm and 50 mm), as well as the effect of changing the emission factor of the energy supply to the building. The simulations have been carried out with three different climates: Oslo in Norway, Prague in the Czech Republic and Rome in Italy.