Two studies were conducted to investigate the relationship between building soiling, stonecleaning, and aesthetic evaluations of architectural facades. In study 1 participants were asked to make evaluations of photographs of architecturally identical facades that varied in terms of level of atmospheric pollution. Significant differences (P<0.01, P<0.05) were found in semantic differential evaluations between cleaned and soiled facades. In study 2 participants were asked to evaluate photographs of buildings according to pollution level, aesthetic value and the degree to which buildings would be aesthetically improved or deteriorate following cleaning. Results showed that in some situations soiling can add to the aesthetic value of buildings. Following from these studies a model is proposed which relates soiling to visual complexity and architectural aesthetics.