A panel which has a central insulating core, usually expanded polystyrene or equivalent material, which core is flanked on one side by a skin laminated to the core, and on the other side by a composite skin such as oriented strand board (OSB) or plywood such as five eighth plywood sheets is disclosed. The oriented strand board is more desirable because of its structure and more importantly its availability in lengths up to forty feet. The joint at the lateral edges is comparable to that of U.S. patent application Ser. No. 513,922 filed Apr. 24, 1990. On one side where there is a protrusion and an interlock with a groove. An extension and recess are provided but the same have a different configuration inasmuch as one has the board substrate is its side portion. In addition, a joiner is provided so that with an overlapping portion of the composite skin on the adjacent laterally disposed panel they will overlap at the middle of the joiner. Since the joiner is secured underneath its overlapping composite skin, simple stapling of the other forms a very tight joint and strengthens when used as a roof. Similarly as a wall, when the OSB or plywood portion is interior, the joint can be strengthened. Another aspect of the invention looks to the provision of a shear rail of the same or equivalent material as the composite skin which is positioned at a mid-station and optionally supplemented by another shear rail at another location in the panel. The shear rails run the length of the panel. This creates an I-beam like effect and permits the panel of a given core thickness to span significantly greater unsupported distances. It also provides for framing a drop in the skylight between parallel rails. The method of the invention looks to the assembly of panels of the type just described into roofs, walls, and building systems.