Airflow rates, hence energy consumption, are directly affected by the amount of open area and consequently by the inhabitant behavior with respect to window opening. This report describes stochastic models using Markov chains, and used to generate time series of window and door openings or window opening angles. It is based on data measured on one hand at he LESO and on the other hand by the TNO Delft on 80 identical, 16 openings dwellings located at Schiedam (NL). The models are validated by a comparison of the real and generated data. The use of these models within building air infiltration design programmes should improve significantly the likelihood of the latter.