To enhance the thermal storage capacity of building envelopes and reduce the energy consumption associated with construction, a composite paraffin room temperature phase change ceramisite for a building envelope was developed. Based on a single factor test method, 52# paraffin and liquid paraffin were heated and melted together to prepare the composite phase change material, which was infiltrated into the ceramisite by vacuum adsorption. The ceramisite adsorbed with paraffin was encapsulated using acrylic emulsion, epoxy resin, or cement paste. The sand in the traditional ceramisite was replaced with the phase change ceramisite to prepare the phase change energy storage mortar for the building application. Using mercury porosimetry, differential scanning calorimetry, and thermal conductivity detection, the phase transition temperature, phase transition latent heat, encapsulation effectiveness, adsorption rate, coefficient of thermal conductivity, and specific heat capacity of the mortar were measured for the phase change ceramisite. The results indicated the following: the phase transition temperature of the composite paraffin could accommodate the range of indoor and outdoor thermal environments (18°C–35°C); a large amount of paraffin could be adsorbed into the ceramisite interior by vacuum adsorption, with the adsorption rate being higher than 58 %; with incorporation of the phase change ceramisite, the coefficient of thermal conductivity of the mortar gradually decreased and the specific heat capacity gradually increased; and when the ceramisite ratio reached 50 %, the coefficient of thermal conductivity decreased by 51.47 % and the specific heat capacity increased by 80.6 %, indicating favorable heat storage performance.