the side edges of the outer metal facing sheet can be of virtually any configuration to facilitate engagement with the exterior joint cover the purpose of which will be discussed hereinafter however as an example of a typical configuration and as a preferred embodiment reference is made to fig1 wherein outer metal facing sheet 13 is provided with a first segment 31 composed of outer metal facing sheet material bent forward inner metal facing sheet 12 second segment 35 is bent substantially parallel to inner metal facing sheet 12 while third segment 32 is bent away from inner metal facing sheet 12 to form a substantially u shaped member structural foam core 11 is generally characterized as possessing top and bottom surfaces which are defined and which are adhesively connected to outer metal and inner metal facing sheets 13 and 12 respectively the structural foam core 11 further possesses a width at its top surface which is substantially coincident with width b which is noted previously is the width of the outer metal facing sheet the bottom surface of structural foam core 11 is substantially coincident with width a the width of inner metal facing sheet 12 as such in gross appearance the side walls of individual structural foam core member 11 slopes diagonally and outwardly from top to bottom as a preferred embodiment the side edge or profile of structural foam core 11 is configured as shown in detail as in fig2 more specifically structural foam core 11 is provided with.