Controlling energy waste from different building bodies plays a key role in energy consumption management. Heat losses in buildings mostly occur through their envelopes and, more particularly, their roofs. Improving the thermal response of roofs is therefore an essential objective. In recent years, the incorporation of Phase Change Materials (PCM) into roof structures has proved to be an effective method in this regard, but still requires further optimization. Here, six different structures of a roof structure, in which PCM capsules have been placed in different positions and orientations, are considered to examine their role as a passive factor in controlling heat loss and increasing thermal resistance. Also, the effect of an external inclined magnetic field on the thermal behavior and energy loss is investigated. The thermal conditions in roofs are reproduced. Governing equations inside the solid parts and the PCM capsules are presented and solved numerically via the finite element method. Streamlines and isotherms, as well as plots of melted volume fraction and thermal resistance are presented. The main outcomes show that the magnetic field has a limited effect on thermal behavior due to the small size of the capsules. Orienting the capsules in the horizontal direction delays heat transmission, slows down the melting, and increases the thermal resistance of the roof structure. PCM melting can be further slowed down by moving the horizontal capsules down, close to the heated boundary. These results can be very useful for future roof designs in which capsules of PCM might be added.
