In this work, we propose a generalized impedance approach to model dissipative interfaces used in vibroacoustic systems, usually composed of poroelastic materials. This approach is based, like the classical impedance approach, on wave propagation. In the usual approach, the impedance is derived by Transfer Matrix Method (TMM) from the knowledge of the waves propagating in the thickness of a laterally infinite medium. Here, using Wave Finite Element Method (WFE), are predicted waves propagating in the thickness of the medium and taking into account the lateral boundaries. It is shown on several examples that these waves make possible to express the contribution of the dissipative layers on master parts, and thus to reduce the size of the global system. Compared to the usual impedance approach, the present method makes possible to use the exact value of the impedance coefficient, taking into account the effect of the lateral boundary conditions and of non-local effects on the response of the system.