This work used a new method for the determination of the mass diffusion coefficients of hygroscopic materials [1]. The experiment consists in submitting one face of the sample to a variation in time of the relative humidity (RH) and measuring the RH on its back face. The imposed RH and temperature are measured during the test and serve as boundary conditions in a comprehensive computational code to solve heat and mass transfer in porous media. This new method was used to characterize a various building materials such as autoclave aerated concrete, plaster, massive wood or wood based materials. This paper includes the determination of sorption isotherms of the selected materials which are needed for the determination of mass diffusivity. The study also confirms that accurate values of mass diffusivity can be obtained even if sample are not at the equilibrium, which allows the characterization time to be drastically reduced.