A past investigation of the flow of hot gases in roof venting led to the development of a simple zone model which for many years has formed the basis for the design of practical roof venting systems. Although calculations of equilibrium depths of the layer of hot gases agree with the results of large-scale experiments, there were no large-scale experiments against which calculations of increase in depth with time could be validated. Recent experiments of Yamana and Tanaka have provided such data and in this paper their results are compared with the predictions of the original model. Calculations have also been made for situations where Yamana and Tanaka did not calculate the increase in depth with time. The correlation is at least as good as that provided by the more recent model of Tanaka and Yamana. There is some evidence that when the layer of hot gases had fallen to within 3 m of the floor of the unvented compartment smoke-logging followed rapidly. This is not predicted by simple models.
