The numerical model for the analysis of the combined convective-conductive heat transfer in the building components has been developed. Presented model is based on the partial differential equation for the two- dimensional steady-state heat transport caused by conduction and convection. The finite element method was used to obtain the numerical solution of the governing equation. The general finite element formulation was derived by means of the Petrov- Galerkin approach. The developed computer program was used to study one typical lightweight building wall construction. The results of simulation demonstrate that the lightweight constructions insulated with permeable mineral wool are very sensitive to the convective heat transfer.