Method for controlling the humidity and the opacity of the walls of a greenhouse, at least one wall being constituted by two membranes arranged one on the other in such a way that the space is created between the said membranes when a fluid under pressure is introduced there, characterised in that the said fluid is sucked out from the said space and led, possibly via a drier, to a heat generator where the said fluid is taken to a temperature which is at least equal to that prevailing inside the greenhouse; the hot fluid is subsequently sent back into the said space, sucked out again and led to the said heat generator, and again pumped back into the said space, this cycle of operations being continued in a closed circuit until the temperature of the fluid in the space and of the said membranes is substantially equal to that which prevails inside the greenhouse; which fluid may also be coloured in order to allow control of the luminous flux passing through the said wall. <IMAGE>
