The role of ventilation in the energy balance of buildings is very important, as well as the need to model the use of lame openings by occupants in energy simulation. Examples of detailed assessment of natural ventilation in overall building thermal simulation procedures are rather rare, especially for long-term evaluation and different types of ventilation. This study addresses this need focusing on natural ventilation modeling in building energy simulation and introducing coupled thermal and ventilation nodal modeling in 1 h simulation steps. All the related parameters are taken into consideration, from wind pressure data to building envelopes and user behavior. The results are validated by conducting experiments on existing constructions and the thermal behavior is monitored and compared in detail in specific building elements. Coupled thermal and ventilation modeling is then implemented to model and assess ventilation strategies for optimum energy-efficient ventilation in a common apartment. These strategies are compared and analyzed for mild Mediterranean and oceanic climates and optimum design procedures are proposed. (C) 2004 Elsevier B.V. All rights reserved.