Abstract: A structural panel material of the sandwich-type construction includes inner and outer facings and a core bonded between the facings. The core includes a plurality of blocks of lightweight core material, such as rigid or semi-rigid plastic foam, balsa wood, or a combination of plastic foam. These blocks are arranged in strips. The strips are joined together by corrugated sheet material. In a preferred embodiment, double-sided corrugated paperboard is used to join the lightweight structural strips. The resulting core material has the highly desirable characteristics of being flexible enough to conform to a mold shape under gravity and with the application of little or no external pressure so that special jigs are not required.

Abstract: A roof structure for a building includes a number of panels, preferably of a sandwich construction with a rigid foam core and upper and lower surfaces which may be metal, wood or other material depending upon the use. A first type of joint extends along the fall line of the roof, with the panels being in side-by-side, spaced relation and supported along their ridges by a roof truss extending along this longitudinal joint. A retainer strip extends along the longitudinal joint and is held in sealing relation with the adjacent panels by means of threaded fasteners secured to the truss. A joint transverse of the fall line is formed by a tongue-in-groove construction of the panels which permits an upper panel to lap over a lower panel for better drainage, and also allows for thermal expansion and contraction.