An isothermal CFD study was made of a building perpendicular to the wind direction. The building was modelled with a closed façade, and consecutively with one and multiple openings. The sensitivity was investigated for different turbulence models, meshes and near wall treatments, both in 2D and 3D. A large sensitivity was found to the modelling options with regard to the predicted wind pressure coefficients (Cp) distribution, but less with regard to the predicted flow rate through the openings. The distribution of Cp was compared to literature and the influence of the openings on the wind pressure coefficients is investigated. Openings have a large influence on local Cp on the windward side, but only limited on the leeward side. The simulated airflow rates were recalculated using theoretical approximation formulas. The calculated values showed better agreement to the CFD-simulations when the Cp in front of the openings were used, compared the Cp taken at a closed wall.