Double-diffusive natural convection in a horizontal enclosure is studied numerically with the use of Boundary Element Method. The enclosure is heated and cooled along vertical walls, while horizontal walls are maintained at different concentration values. The Brinkman model is used to simulate the fluid flow through porous media, the density variation is taken into account by the Boussinesq approximation. The governing parameters of the problem are the Darcy number, porous Rayleigh number, Lewis number and buoyancy coefficient. Different flow regimes for thermal and solutal dominated flows are demonstrated for different values of governing parameters. The results are compared to those in published studies, obtained with other approximative methods.