This paper describes a general thermodynamic model, including the constitutive equations, and applies it to the coupled heat and moisture transfer in porous building materials. The resulting balance equation system and the constitutive equations for the quantities considered can be numerically solved. The constitutive equations describe the phase-divided moisture transport (liquid water flux and water vapor diffusion/advection) leading into phase-divided defined hygric transport coefficients of the balance equation system. Currently, it is impossible to separate liquid water flux and water vapor transport experimentally. To circumvent these difficulties, moisture conductivities and a phase-dividing function are introduced. For a known phase-dividing function, the phase-divided defined transport coefficients of the balance equation system can be calculated from the measured moisture conductivities. The paper presents a numerical investigation of a phase-dividing function evaluation and a description of laboratory experiments required for material characterization.