A door or window sash comprising at least: - a main body having an insulating chamber bilaterally obtained from corresponding glazing panels (3, 4) whose size is larger than the size of the chamber so as to form a perimetric compartment open towards the outside; the first glazing panel being larger in the dimensions of its perimeter than the second glazing panel so that it projects from the bottom of the compartment to a depth which is greater than the depth of the second glazing panel; - a rigid inner frame composed of a profiled section (7, 8) for each side of the compartment and housed inside the selfsame perimetric compartment; each profiled section (7, 8) being joined at the ends of it to corresponding contiguous profiled sections (8, 7) through the agency of respective joint means; - each of the profiled sections (7, 8) defining an accessorized zone, open to the outside, housing hinge means which, in use, connect the main body along a vertical axis to a fixed frame, and housing also means which, in use, operate and/or drive the sash in such a way as to allow it at least to turn about the vertical axis in order to define an open and a closed configuration of the door or window, the joint means comprising a reference and joining member for each pair of ends of the profiled sections (7, 8); said reference and joining member comprising a first wing and a second wing, protruding from the angled surfaces of the central body and configured to be coupled within tubular chambers (7a, 8a) formed by the corresponding profiled sections (7, 8), characterised in each reference and joining member having at least: - a central body provided with two contact surfaces, at an angle to each other, for the corresponding ends of the profiled sections (7, 8) to be joined and in such a way as to form a corner for joining the frame; - at least a third wing protruding laterally from one end of the central body and configured to contain, in abutment, the edges of the corner of the second glazing panel in such a way as to define an external reference point when the reference and joining member is placed in the compartment, wherein the central body comprises a front inside wall configured for stable contact, in use, with at least one corner surface of the insulating chamber in such a way as to define a third reference point during placement in the compartment. - a main body having an insulating chamber bilaterally obtained from corresponding glazing panels (3, 4) whose size is larger than the size of the chamber so as to form a perimetric compartment open towards the outside; the first glazing panel being larger in the dimensions of its perimeter than the second glazing panel so that it projects from the bottom of the compartment to a depth which is greater than the depth of the second glazing panel; - a rigid inner frame composed of a profiled section (7, 8) for each side of the compartment and housed inside the selfsame perimetric compartment; each profiled section (7, 8) being joined at the ends of it to corresponding contiguous profiled sections (8, 7) through the agency of respective joint means; - each of the profiled sections (7, 8) defining an accessorized zone, open to the outside, housing hinge means which, in use, connect the main body along a vertical axis to a fixed frame, and housing also means which, in use, operate and/or drive the sash in such a way as to allow it at least to turn about the vertical axis in order to define an open and a closed configuration of the door or window, the joint means comprising a reference and joining member for each pair of ends of the profiled sections (7, 8); said reference and joining member comprising a first wing and a second wing, protruding from the angled surfaces of the central body and configured to be coupled within tubular chambers (7a, 8a) formed by the corresponding profiled sections (7, 8), - a central body provided with two contact surfaces, at an angle to each other, for the corresponding ends of the profiled sections (7, 8) to be joined and in such a way as to form a corner for joining the frame; - at least a third wing protruding laterally from one end of the central body and configured to contain, in abutment, the edges of the corner of the second glazing panel in such a way as to define an external reference point when the reference and joining member is placed in the compartment, wherein the central body comprises a front inside wall configured for stable contact, in use, with at least one corner surface of the insulating chamber in such a way as to define a third reference point during placement in the compartment.