In determining the effect of surface roughness of external finish material on the solar energy gain of opaque building surfaces, the topography of the surface material has to be investigated in derail and the roughness level has to be expressed as a standard parameter. In this study the roughness levels of external finish materials with the same white colour and structure, are evaluated by a close-range photogrammetric method. The roughness parameter (R(a)) is calculated according to the data obtained by the photogrammetric application. The solar energy gain of opaque surfaces is determined by the solar absorptance of the material. The solar absorptance of the material is evaluated by experimental method and the relationship between the solar absorptance and surface roughness is suggested. Copyright (C) 1996 Elsevier Science Ltd.