A method and apparatus for simulating occupant behavior in buildings may be used to predict the energy use of a building structure. The activities of actual building occupants are recorded and provided as an input to the occupant behavior simulation. The occupant behavior simulation generates simulated occupant schedules with similar behavioral patterns. An arbitrary set of factors can be used to select plausible activity types, durations, and numbers of participants during an occupant behavior simulation. The simulated occupant schedules may then be incorporated into a building performance simulation to help architects predict the energy demand associated with different building design options.