New technologies are needed in structures and services in order to reduce the great energy consumption of buildings. A major share of the energy demand is used for controlling the indoor climate. The requirements are only growing due to tightening regulation and increasing comfort expectations of the users. The wide use of air conditioning systems illustrates this trend. Phase Changing Materials (PCM) open an alternative potential to return a part of cooling needs based upon melting and solidifying properties of some special components within a room temperature range. Thanks to this phenomenon, some degrees of additional control can be achieved. Experimental results from laboratory tests and monitoring results in two rooms of two actual buildings presented in this paper show that gypsum plaster finishings with a thin layer of 5 mm of PCM are favourable to achieve 2 to $5^{circ}C$ reduction in the temperature swing in rooms.