In this work, we review the environmental needs, natural ventilation installations and housing design for fattening lambs. The optimum temperature range for fattening lambs was shown to be between 10 and 20°C. We also found that in winter, a higher indoor temperature in the fattening unit reduces the need for housing ventilation, which minimises heat loss and facilitates maintenance of a higher indoor temperature. In summer, the problem is the high outdoor temperature which, due to climate change in southern Europe, is tending to increase year upon year with more extreme thermal values, which becomes very important when designing feedlots in a large part of the Iberian Peninsula. The dimensions of buildings, their location, thermal insulation, natural ventilation design and the possibility of using evaporative cooling are aspects to consider.