This poster presents an experiment on judgments of design complexity, based on two modes of stimuli: the layouts of corridor systems in buildings shown in plan view and movies of simulated walkthroughs. Randomly selected stimuli were presented to 166 subjects: ‘experts’ (architects or students currently enrolled on an architectural course) and ‘lay people’ (all others). The aims were to investigate whether there were differences between these two groups in terms of their judgments of building complexity, effects of modality of stimuli and if any environmental measures (geometric or complexity-based) correlated with the assessments. The results were, first, there are differences between the judgments of the experts and non-experts, second, the effect of modality was negligible for lay people but evident for the ‘experts’, third, the judgments of both groups correlated highly with a number of environmental measures.