The roughness extension of Knopp, Eisfeld and Calvo (KEC)  for
type turbulence models has been applied to the flow through rough pipes, over a flat plate and around the NACA 65
-215 airfoil with a rough surface. The results are compared to predictions using the boundary condition originally devised by Wilcox  for rough surfaces, and to predictions with the Spalart-Allmaras model with the Boeing roughness extension by Aupoix and Spalart (ASB) . Good agreement with experiments has been achieved with respect to the influence of the roughness on the velocity profile, the skin friction coefficient and the loss in lift.