The energy use of buildings is almost one-third of the global final energy use. Phase change Materials (PCMs) are substances that undergo phase transition when the surrounding temperature reaches their phase transition temperature. PCMs are reported to be a good candidate as a thermal storage buffer in building systems. Accordingly, PCMs may be able to regulate the indoor temperature while using less energy and thereby contributing in improving the energy performance of the building. In this project a trail to analyse the effect of PCMs in indoor temperature was carried out, in an experimental set-up, using a climate chamber. The chamber temperature is regulated as a sinusoidal profile with a cycle of 24 hours, with a maximum of 40 °C and a minimum of -10 °C. A cubic-box, is placed at the centre of the chamber, and is used as a representation of “building”. A board was made by encapsulating PCMs, with a melting temperature of 24 °C, to gypsum with a fraction of 20 wt%. The influence of PCM added gypsum board on inside temperature of the box is studied. Temperatures at different locations have been measured by thermocouples. The results indicated that the presence of PCM resulted in less temperature variation inside the box with the temperature holding close to the PCM transition temperature for a long period. Also, the PCM boards shifted the temperature profile. Further results are expected to determine the location of the PCM board that is most suitable to reduce the temperature variation inside the building.