Zero-pressure gradient boundary layers over high-skewness surfaces are studied via direct numerical simulations (DNS) in computational domains of up to 135δ long with friction Reynolds numbers up to Reτ ≈ 4, 500. Monoculture and multiculture biofouling-type surfaces were utilized at a planar solidity of approximately λp ≈ 40%. It is found that both the evolution of the main boundary layer quantities, as well as of the total drag, scale with the mean roughness height, h, regardless of the roughness element shape and distribution. The same conclusions are made with respect to the roughness function ∆U [+]. The outer-layer similarity is also investigated under different scalings and verified in both the first and second order turbulence statistics. Furthermore, the roughness impact on the flow dynamics in both a quantitative and qualitative manner is also explored by means of quadrant analysis. Finally, an attempt is made towards adapting the Schlichting’s boundary layer equations for rough-walls through a height-based occupancy ratio, that successfully captures most of the DNS-expected boundary layer evolutions.