Most commercially available wall functions for k-e turbulence models base on the two-zonal near-wall flowdivision assumption. Viscous and log-law sublayers are distinguished. In this article the three-zonal wall function conceptwith a buffer sublayer is developed. The aim of this new wall function is to improve the mean streamwise U+ velocity profile.The proposed wall function is validated on backward-facing step experimental data. Physical implications of the modelperformance are also discussed.