Abstract: Composite building structures, such as foam core panels or the like. The panels comprise one or more foam core sections, preferably cores which include fire retardant additives. The exterior sheathing for the foam cores is a multiple laminate containing an inorganic filler material, such as glass fibers or ground carbonaceous or siliceous material; the filler is bound in place by a fire retardant, furan-based resin. The method includes forming a plurality of layers by depositing the resin and the filler alternately in a mold, thereafter placing boards or like core structures thereover and covering the exposed surfaces by multi-ply laminates of the fire retardant furan-based resin containing the glass fiber, carbonaceous or siliceous fillers. The method is also applicable to cover existing foam core installations used in building structures.