It is often claimed that architects rely on their own ex periences of space usage when designing houses for others. If so, architects who use houses in ways that differ from non-architects are likely to produce designs that are not representative of their client's lifestyles. An experiment was carried out to evaluate the nature of the differences between architects and non-architects in their space usa ge patterns. The two groups (10 in each) were asked to ra te the likelihood of occurrence, for both day and evening usage, of 15 behaviours in 15 spaces (indoor and outdoor) of a house. An INDSCAL analysis produced an interpretable 4-dimensional solution: I - Motor/Expressive Activity; II - Intimacy of Social Interaction; III - Activities As sociated with Eating; IV: Verbal/Expressive Activity. Architects placed a heavy emphasis on the first two dimen sions, non-architects attaching more importance to dimen sions III and IV. The relative importance of the dimen sions depended on time of day for architects but not for non-architects.