Self-supporting timber box having a base panel, lateral walls each projecting perpendicularly from one side of the base panel to delimit the profile of an internal space of the box, a plurality of internal partitions (14) which are parallel to each other and perpendicular to the base panel and which extend between the lateral walls in such a way as to divide the internal space into a plurality of compartments intended to receive a heat-insulating lining, and a cover panel, wherein it has at least one stiffening element (16) which is positioned in the internal space transversely with respect to the internal partitions and which has an area of connection (17, 18) to each of the internal partitions to increase the buckling resistance of the internal partitions, the area of connection extending over a depth greater than or equal to half of the distance between the base and cover panels.