Windows are one of the major means by which building occupants control the indoor environment. This research uses results from ﬁeld surveys to formulate a method for simulation of ofﬁce buildings to include the effects of window opening behaviour on comfort and energy use. The paper focuses on: (1) what is general window opening behaviour? (2) how can we frame an ‘‘adaptive algorithm’’ to predict whether windows are open?(3) how can the algorithm be used within a simulation to allow the effects of window opening on comfort and energy use to be quantiﬁed? We havefound that: (1) the proportion of windows open depends on indoor and outdoor conditions, (2) logistic regression analysis can be used to formulatean adaptive algorithm to predict the likelihood that windows are open, (3) the algorithm when embedded in simulation software provides insightsnot available using more usual simulation methods and allows the quantiﬁcation of the effect of building design on window opening behaviour, occupant comfort and building energy use.