The roughness length, and displacement height, characterize the resistance exerted by the roughness elements on turbulent flows and provide a conventional boundary condition for a wide range of turbulent-flow problems. Classical laboratory experiments and theories treat them as geometric parameters independent of the characteristics of the flow. In this paper, we demonstrate essential stability dependences – stronger for the roughness length (especially in stable stratification) and weaker but still pronounced for the displacement height. We develop a scaling-analysis model for these dependences and verify it against experimental data.