This study investigated the feasibility of reducing energy demand in residential buildings using a new material called “Phase Change Material with Mycelium Integration (PCMMI)”, considering the climatic conditions in Jordan, Amman. A numerical simulation was conducted (through Autodesk-Revit program) to compare the thermal performance of a simulated residential building with currently used construction materials, and the thermal performance of the same building using PCMMI. The results of the numerical simulation showed that the main three components of the residential building: the external walls W.01, the roof R.01, and the ground floor slab S.01 all did not meet the regulated codes without the new material. The codes specified the value of the thermal transmittance (U-Value). The thermal performance of the building’s envelope was enhanced by adding the PCMMI layer. The results of the calculations illustrated that the PCMMI helped the residential building envelope thermal performance by reducing the U-Value and meeting the limit of the codes of Jordanian regulations of thermal insulation.