At present, non-renewable energy sources such as oil are being consumed in large quantities and, along with this energy consumption, large quantities of carbon dioxide (greenhouse gases) are being produced, contributing to increased global warming. The energy used to control the interior temperature of a building area cannot be disregarded since the building industry, as a significant energy consumer and CO2 emitter, has a significant influence on the reduction of greenhouse gas emissions. Due to their enormous thermal energy storage capacity, phase change materials may be employed in building envelopes, where they can help conserve energy and somewhat lower carbon emissions. In this paper, the thermal performance of phase change materials that can be applied to the building sector is summarised and compared, while various ways of improving the ratio of thermal efficiency to cost are proposed based on their practical use, from material enhancement, production method enhancement, and the choice of use and location for efficiency enhancement.