Recently, issues regarding health problems related to dampness in buildings have been widely reported in Europe and America. In some studies, a moisture buffer effect that provides passive moisture control using interior materials was proposed as an effective way to alleviate such dampness problems. Until now, in order to evaluate the moisture buffer effect, a simulation model that assumes the indoor air temperature and humidity to be uniform (complete diffusion) has been widely used. However, when using this method, it is difficult to evaluate the influence of vapor distribution near materials and the contribution of materials in different positions of a room space. In this paper, the authors propose a new CFD simulation model incorporating a coupled simulation method with convection and heat and vapor transportation through interior building materials.