The invention relates to greenhouses of the sort with opening roof structures capable of providing ventilation and, above all, of saving the structure of the greenhouse by discharging any load capable of becoming critical by building up on the roof structure and on the gutters. The greenhouse according to the invention is essentially characterised in that the ridge articulation (10) of the two main rafters (3) belonging to the same truss moves, about a vertical axis, by means of a guide made up of the moving part (11) of the (king) post (4) and in that, simultaneously, the two lower ends of the said main rafters move, along a horizontal axis, by means of a guide made up of a rail (12) secured to the top of the main tie beam (2) in which the said ends move, which include rolling means (13). <IMAGE>
