The procedure commonly used for calculating environmental control of animal houses in hot climates is based on removing sensible internal heat by means of ventilation on the assumption that in a stationary situation the inside temperature is 2-3 degrees C greater than outside. This procedure, at least in warm-temperate climates, has been called into question by the results of numerous experiments in which inside temperatures below the outside temperatures were recorded, during the hottest part of the day. This study aims to analyse this question on a theoretical and experimental basis and to establish a method of calculation that is more suitable for actual situations. in fact, the heat created inside the building by the solar radiation on the one hand, and on the other hand the heat removed by evaporation inside the building of the extensive wet surfaces appear to be of great importance. This method enables the efficacy of the different project options to be more accurately assessed, in particular the importance of the orientation of the buildings in order to both reduce solar radiation and increase the cooling effect of evaporation by better exploiting prevailing winds.