Disclosed is a system for constructing a habitable room or the like including at least one door, walls, and door mount to pivot relative to the two walls about an axis in such a manner as to be suitable for occupying at least two positions, namely a “closed” position in which the door is contained in the plane of the first wall, and an “open” position in which the door is not. The system includes a through opening and a setback each presenting a shape substantially complementary to the door and made respectively in the first and second walls, and together having a common zone, with the axis in the zone, and arranged in such a manner that, on pivoting about the axis, the door in its first position it is integrated in the opening, and when it is in its second position, it is contained in the setback.