A model for calculating surface roughness effect on the intensity of emitted X-rays in the soft and ultrasoft X-ray region is presented and discussed. The results of calculations based on this model are compared to the results obtained experimentally using At grating as models for rough surfaces. It is shown that the correspondence between calculated and experimental intensities for Al-K is sufficient to corroborate the use of this model as a means of estimating maximum allowable surface roughness without a significant loss in intensity. It is also shown that this maximum allowable roughness estimate can be calculated with a knowledge of only the sample density and wavelength of the X-ray emission.