In this paper, the existing numerical methods to simulate phase change materials (PCMs) embedded in building structures are reviewed and two forms of the modelling scheme are explained in detail. The first formulation is a noniterative temperature formulation which suffers from the requirement of extremely small time steps to produce accurate results. The second formulation is an iterative enthalpy formulation which through the use of an iterative correction scheme at every time step, can produce fairly accurate results for comparatively much larger time step values. A customized building simulation code was developed in MATLAB to incorporate the correction scheme. The simulation results were compared with ESP-r for the standard BESTEST Case 600 model. It was found that there was significant discrepancy in temperature profiles at large time step values when PCMs were introduced. However, the difference became smaller when the time steps in ESP-r was reduced while keeping it same in the MATLAB model.