Analyses theoretically the natural ventilation of buildings. Derives fundamental formula for the amount of ventilation due to temperature difference from Bernouilli's theorem considering buoyancy. Explains physical meaning of friction loss and theneutral zone, derives pressure distribution due to wind from the shape of buildings and the location of openings. Obtains total expression for amount of ventilation due to both temperature difference and wind. Discusses method of measuring air flow using carbon dioxide as a tracer gas and describes experiments on models with inside temperature higher than outside. Describes experiment to measure discharge coefficient of various forms of crack or opening and experiment in model on wind tunnel where internal and external wind velocities were measured. Compares experimental results to theoretical prediction.