In this paper, the existing numerical methods to simulatephase change materials (PCMs) in building simulations arereviewed and two forms of the modeling scheme are explainedin detail. The first formulation is a non-iterative temperatureformulation which suffers from the requirement of extremelysmall time steps to produce accurate results. The secondformulation is an iterative enthalpy formulation which throughthe use of an iterative correction scheme at every time step, canproduce fairly accurate results for comparatively much largertime step values. A customized building simulation code wasdeveloped in MATLAB to incorporate the correction scheme.The simulation results were compared with ESP-r for the standardBESTEST Case 600 model. It was found that there wassignificant discrepancy in temperature profiles at large timestep values when PCMs were introduced. However, the differencebecame smaller when the time steps in ESP-r was reducedwhile maintaining the large time step in the MATLAB model.