In the vadose zone, fluids, which can transport contaminants, move within unsaturated rock fractures. Surface roughness has not been adequately accounted for in modeling movement of fluid in these complex systems. Many applications would benefit from an understanding of the physical mechanism behind fluid movement on rough surfaces. Presented are the results of theoretical investigation of the effect of surface roughness on fluid spreading. The model presented classifies the regimes of spreading that occur when fluid encounters a rough surface: i) microscopic precursor film, ii) mesoscopic invasion of roughness and iii) macroscopic reaction to external forces. Theoretical diffusion-type laws based on capillarity and fluid and surface frictional resistive forces developed using different roughness shape approximations are compared to available fluid rise on roughness experiments. The theoretical diffusion-type laws are found to be the same apparent functional dependence on time; methods that account for roughness shape better explain the data as they account for more surface friction.